Multi-axis coil for implantable medical device

ABSTRACT

Systems, devices and methods allow inductive recharging of a power source located within or coupled to an implantable medical device while the device is implanted in a patient. The implantable devices in some examples include a multi-axis antenna having a plurality of coil windings arranged orthogonal to one another. The multi-axis antenna configured to generate at least a minimum level of induced current for recharging a power source of the implanted medical device regardless of the orientation of a direction of a magnetic field imposed on the multi-axis antenna relative to an orientation of the implanted medical device and the multi-axis antenna for a given energy level of the imposed magnetic field.

This application is a continuation of U.S. patent application Ser. No.16/021,059, filed Jun. 28, 2018, the entire content of which isincorporated herein by reference.

TECHNICAL FIELD

The disclosure relates to devices and systems used to recharge a powersource located within a medical device that has been implanted in apatient.

BACKGROUND

Various implantable medical devices have been clinically implanted orproposed for therapeutically treating or monitoring one or morephysiological and/or neurological conditions of a patient. Such devicesmay be adapted to monitor or treat conditions or functions relating toheart, muscle, nerve, brain, stomach, endocrine organs or other organsand their related functions. Advances in design and manufacture ofminiaturized electronic and sensing devices have enabled development ofimplantable devices capable of therapeutic as well as diagnosticfunctions such as pacemakers, cardioverters, defibrillators, biochemicalsensors, implantable loop recorders, and pressure sensors, among others.Such devices may be associated with leads that position electrodes orsensors at a desired location, or may be leadless with electrodesintegrated into the device housing. These devices may have the abilityto wirelessly transmit data either to another device implanted in thepatient or to another instrument located externally of the patient, orboth.

Although implantation of some devices requires a surgical procedure(e.g., pacemakers, defibrillators, etc.), other devices may be smallenough to be delivered and placed at an intended implant location in arelatively noninvasive manner, such as by a percutaneous deliverycatheter, or transvenously. By way of illustrative example, implantableminiature sensors have been proposed and used in blood vessels tomeasure directly the diastolic, systolic and mean blood pressures, aswell as body temperature and cardiac output of a patient. As oneexample, patients with chronic cardiovascular conditions, particularlypatients suffering from chronic heart failure, may benefit from the useof implantable sensors adapted to monitor blood pressures. As anotherexample, subcutaneously implantable monitors have been proposed and usedto monitor heart rate and rhythm, as well as other physiologicalparameters, such as patient posture and activity level. Such direct invivo measurement of physiological parameters may provide significantinformation to clinicians to facilitate diagnostic and therapeuticdecisions. In addition, miniaturized pacemakers that may be implanteddirectly within a patient's heart with or without the need for externalleads, have been proposed, built, and adapted to provide both pacing andother electrical therapy to the patient.

SUMMARY

The disclosure describes implantable medical devices, systems, andassociated techniques, structures, and assemblies configured to providerecharging of power sources located within medical devices that havebeen implanted within a patient. The implanted medical devices includingthese power sources that are to be recharged are often small devicesthat have been implanted relatively deeply within the patient, forexample implanted internally within the heart of a patient. An exampleof such a device is the Medtronic® Micra™ self-contained pacemaker thatis designed to be implanted internally, for example within a chamber ofthe heart of a patient, and in various examples requires no externalleads coupled to the device in order to provide pacing and electricalstimulation to the heart.

The implanted devices may include a multi-axis receive antennacomprising of one or more coils coupled to recharging circuitry andconfigured to have currents induced into one or more of the coils toprovide a recharging current for recharging a power source of theimplanted medical device. Examples of multi-axis antennas as describedherein provide a compact and efficient receive antenna that may belocated within a housing of an implantable medical device, includingversions of miniaturized implantable medical devices such as theMedtronic® Micra™ self-contained pacemaker. In some examples, themulti-axis antenna includes an antenna core formed from a ferritematerial, which may have a cubic shape, with a first coil, a secondcoil, and a third coil, each coil having a normal axis of orientationthat is orthogonal to the normal axis of each of the other coils, andformed to encircle a portion of the antenna core. Additional circuitrythat includes individual diodes coupled to each coil may be arranged torectify and to sum together the current or currents induced into the oneor more of the coils in order to provide a recharging current that maybe applied to a power source of the implanted medical device. Therecharging current may be utilized to recharge the power source, and/orto power the operation of the implanted medical device.

When there is a need to recharge these implantable medical devices, thedevice including the multi-axis antenna may be placed within a magneticfield (or within a resultant magnetic field formed by a plurality ofmagnetic fields), which is generated by an externally powered device andone or more recharging coils so that the magnetic field (or theresultant magnetic field) is imposed onto the multi-axis antenna of theimplanted medical device being recharged. The magnetic field imposed onthe multi-axis antenna is arranged to induce electrical current into oneor more of the coils of the multi-axis antenna. The induced electricalcurrent or currents may be used to recharge a power source of theimplanted medical device and/or to provide the electrical power used todirectly operate the device. Examples of the multi-axis antenna asdescribed in this disclosure may provide at least a minimum level ofrecharging current induced into the one or more coils of multi-axisantenna for a given energy level of the magnetic field imposed on themulti-axis antenna regardless of the orientation of a direction of themagnetic field relative to the orientation of the device and themulti-axis antenna.

The multi-axis antenna may have an ability to induce currents forrecharging purposes irrespective of the orientation of the direction ofthe magnetic field relative to the orientation of the device and themulti-axis antenna, which may allow for recharging the implanted medicaldevice using a simplified recharging system. In some examples,recharging of the implanted medical device may be accomplished usingonly a single planar recharging coil generating the magnetic field, orfor example using just a single pair of recharging coils, to achieverapid recharge of the implanted medical device without the need forelaborate orientation procedures and/or complex orientation equipment.

Examples described in this disclosure are directed to a method forrecharging a power source located in an implanted medical deviceimplanted in a patient, the method comprising receiving, at a multi-axisantenna of an implantable medical device, a magnetic field having amagnetic field direction, the magnetic field generated by at least onerecharging coil, wherein the magnetic field induces one or moreelectrical currents in one or more of a plurality of coils forming themulti-axis antenna, the plurality of coils comprising a first coilhaving a first coil axis of orientation, a second coil having a secondcoil axis of orientation, and a third coil having a third coil axis oforientation, wherein the first coils axis of orientation and the secondcoil axis of orientation and the third coil axis of orientation areorthogonal to each other, wherein each of the first coil, the secondcoil, and the third coil encircle a portion of a ferrite core, andwherein the third coil encircles at least a portion of the first coiland the second coil, and wherein the second coil encircles at least aportion of the first coil. The method also includes summing, byrecharging circuitry, the one or more electrical currents induced intothe plurality of coils to form a recharging current; and applying, bythe recharging circuitry, the recharging current to the power source ofthe implantable medical device to recharge the energy level stored inthe power source.

Examples described in this disclosure also include an implantablemedical device comprising a rechargeable power source coupled to one ormore electrical circuits located within a housing of the implantablemedical device, the rechargeable power source configured to provideelectrical power to the one or more electrical circuits, and amulti-axis antenna comprising a plurality of coils encircling a ferritecore, the multi-axis antenna configured to generate a recharging currentfrom one or more electrical currents induced into one or more of theplurality of coils when an externally generated magnetic field having amagnetic field direction is imposed onto the multi-axis antenna, themulti-axis antenna positioned within the housing of the implantablemedical device and encircled by an antenna window forming a portion ofthe housing, the antenna window formed from a material that is radiotransmissive, wherein the plurality of coils comprises a first coilhaving a first coil axis of orientation and formed from firstelectrically conductive winding, a second coil having a second coil axisof orientation and formed from a second electrically conductive winding,and a third coil having a third coil axis of orientation and formed froma third electrically conductive winding, the first coil axis oforientation, the second coil axis of orientation, and the third coilaxis of orientation orthogonal to each other. The implantable medicaldevice also includes recharging circuitry coupled to the multi-axisantenna and to the rechargeable power source, the recharging circuitryconfigured to receive the one or more electrical currents induced intoone or more of the plurality of coils and to provide a rechargingcurrent to the rechargeable power source comprising a sum of the one ormore electrical currents induced in one or more of the plurality ofcoils, wherein the multi-axis antenna and the recharging circuitry areconfigured to provide at least a minimum level of recharging current fora minimum level of power provided by the magnetic field imposed on themulti-axis antenna for any random orientation of the direction ofmagnetic field relative to an orientation of the implanted medicaldevice.

Examples described in this disclosure also include a recharging systemfor recharging a power source located in an implanted medical deviceimplanted in a patient, the recharging system comprising an electricalpower source, at least one recharging coil coupled to the electricalpower source and configured to generate a magnetic field having amagnetic field direction when electrically energized by the electricalpower source, a multi-axis antenna located in the implantable medicaldevice, the multi-axis antenna comprising a plurality of coilsconfigured to generate a recharging current when the magnetic fieldgenerated by the at least one recharging coil is imposed onto themulti-axis antenna, wherein the plurality of coils comprises a firstcoil having a first coil axis of orientation, a second coil having asecond coil axis of orientation orthogonal to the first coil axis oforientation, and a third coil having a third coil axis of orientatingthat is orthogonal to the both the first coil axis of orientation andthe second coils axis of orientation, and wherein the third coilencircles at least a portion of the first coil and the second coil andthe second coil encircles at least a portion of the first coil. Therecharging system also includes recharging circuitry coupled to themulti-axis antenna, the recharging circuitry configured to sum one ormore currents induced into one or more of the first coil, the secondcoil, and the third coil to generate the recharging current; and aswitching device coupled to the multi-axis antenna and the power sourceof the implanted medical device, the switching device configured to becontrolled by the recharging circuitry to couple the recharging currentto the power source to recharge the electrical energy stored in thepower source.

Examples described in this disclosure further include a passiveimplantable medical device comprising a multi-axis antenna comprising aplurality of coils encircling a ferrite core, the multi-axis antennaconfigured to generate an operating current from one or more electricalcurrents induced into one or more of the plurality of coils when anexternally generated magnetic field having a magnetic field direction isimposed onto the multi-axis antenna, the multi-axis antenna positionedwithin the housing of the implantable medical device and encircled by anantenna window forming a portion of the housing, the antenna windowformed from a material that is radio transmissive, wherein the pluralityof coils comprises a first coil having a first coil axis of orientationand formed from first electrically conductive winding, a second coilhaving a second coil axis of orientation and formed from a secondelectrically conductive winding, and a third coil having a third coilaxis of orientation and formed from a third electrically conductivewinding, the first coil axis of orientation, the second coil axis oforientation, and the third coil axis of orientation orthogonal to eachother. The passive implantable medical device also includes electricalcircuitry coupled to the multi-axis antenna, the electrical circuitryconfigured to receive the one or more electrical currents induced intoone or more of the plurality of coils and to electrically power andoperate the passive implantable medical device using the operatingcurrent provided by the multi-axis antenna, the operating currentcomprising a sum of the one or more electrical currents induced in oneor more of the plurality of coils, wherein the multi-axis antenna isconfigured to provide at least a minimum level of recharging current fora given level of power provided by the magnetic field imposed on themulti-axis antenna for any random orientation of the direction ofmagnetic field direction relative to an orientation of the implantedmedical device.

Examples described in this disclosure also include a method A methodcomprising receiving, at a multi-axis antenna of a passive implantablemedical device, a magnetic field having a magnetic field direction, themagnetic field generated by at least one recharging coil, wherein themagnetic field induces one or more electrical currents in one or more ofa plurality of coils forming the multi-axis antenna, the plurality ofcoils comprising a first coil having a first coil axis of orientation, asecond coil having a second coil axis of orientation, and a third coilhaving a third coil axis of orientation, wherein the first coils axis oforientation and the second coil axis of orientation and the third coilaxis of orientation are orthogonal to each other, wherein each of thefirst coil, the second coil, and the third coil encircle a portion of aferrite core, and wherein the third coil encircles at least a portion ofthe first coil and the second coil, and wherein the second coilencircles at least a portion of the first coil. The method furtherincludes summing, by electrical circuitry, the one or more electricalcurrents induced into the plurality of coils to form an operatingcurrent; and applying, by the electrical circuitry, the operatingcurrent to the electrical circuitry of the passive implantable medicaldevice to electrically power and operate the passive implantable medicaldevice, the operating current comprising a sum of the one or moreelectrical currents induced in one or more of the plurality of coils,wherein the multi-axis antenna is configured to provide at least aminimum level of operating current for a minimum level of power providedby the magnetic field imposed on the multi-axis antenna for any randomorientation of the direction of magnetic field direction relative to anorientation of the implanted medical device.

This summary is intended to provide an overview of the subject matterdescribed in this disclosure. It is not intended to provide an exclusiveor exhaustive explanation of the apparatus and methods described indetail within the accompanying drawings and description below. Thedetails of one or more aspects of the disclosure are set forth in theaccompanying drawings and the description below.

BRIEF DESCRIPTION OF THE FIGURES

The details of one or more examples of this disclosure are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of this disclosure will be apparent from thedescription and drawings, and from the claims.

FIG. 1 is a conceptual drawing illustrating an example medical devicesystem in conjunction with a patient according to various examplesdescribed in this disclosure.

FIG. 2 is a conceptual drawing illustrating an example configuration ofan implantable medical device according to various examples described inthis disclosure.

FIG. 3 is a schematic diagram including a three-axis antenna coupled toa rechargeable power source of an implantable medical device accordingto various examples described in this disclosure.

FIG. 4 is an exploded view and an assembled view of a multi-axis antennaaccording to various examples described in this disclosure.

FIG. 5 illustrates a set of graphical diagrams of magnetic fieldintensities versus induced power as provided by individual coils and acombination of coils of a multi-axis antenna according to variousexamples described in this disclosure.

FIG. 6 is a functional block diagram of an intracardiac pacing deviceaccording to various examples described in this disclosure.

FIG. 7 is a functional block diagram illustrating an exampleconfiguration of a system for inductive recharging of an implantablemedical device according to various examples described in thisdisclosure.

FIG. 8 is a functional block diagram illustrating an example inductiverecharging system according to various examples described in thisdisclosure.

FIG. 9 illustrates graphs of representative waveforms that may begenerated by a signal generator and applied to the recharging coil orcoils of a recharging system according to various examples described inthis disclosure.

FIG. 10 is a flowchart illustrating a method according to variousexamples described in this disclosure.

FIG. 11 is a flowchart illustrating a method according to variousexamples described in this disclosure.

In the figures, use of a same reference number or a same referencenumber with a letter extension may be used to indicate a same orcorresponding device or element when used in a same drawing or indifferent drawings. In addition, unless otherwise indicated, devicesand/or other objects such as a patient, an implantable medical device,or an electrical device such as an electrical coil, are not necessarilyillustrated to scale relative to each other and/or relative to an actualexample of the item being illustrated. In particular, various drawingsprovided with this disclosure illustrate a “patient” represented by ahuman-shaped outline, and are not to be considered drawn to scalerelative to an actual human patient or with respect to other objectsillustrated in the same figure unless otherwise specifically indicatedin the figure for example by dimensional indicators, or for example asotherwise described in the text of the disclosure.

DETAILED DESCRIPTION

Traditional pacemakers, neurostimulators and implantable loop recordersmay use primary batteries with finite energy as an internal power sourcefor electrically powering operation of the device once the device hasbeen implanted in a patient. In various examples of implanted medicaldevices, a primary (non-rechargeable) battery has a finite energyreservoir which limits its mission life based on its size and energydensity (for a given energy usage rate). This limits the useful durationof the implanted device. Once a primary battery is exhausted,replacement of the device may be required, and although replacement ofthe device may be minimally invasive, it may still be traumatic to thepatient. For example, risk of a pocket infection in the area of theimplant may occur, which in turn may lead to longer hospital stays andincreased cost burden to the patient and/or the insurance companies.

In addition, limits on the available battery energy may result in limitsto therapy options for a device and/or the patient. Further, issuesrelated to the implanted medical device may result in a need for a moreenergy consuming device configuration, which can further shorten themission life of the implanted device. For example, for a percentage ofpatients, e.g., for twenty five percent of patients implanted with aleft ventricle (LV) lead, the patient does not respond to cardiacresynchronization therapy (CRT) due to sub-optimal lead placement,resulting in the need to apply higher levels of stimulation thresholds,causing excessive battery drain and reduced longevity of the implanteddevice.

The use of rechargeable batteries or other rechargeable power sourcesthat can be located within an implantable medical device and utilized topower the operation of the device is not a novel concept for overcomingthe issues of limited energy primary batteries. However, use ofrechargeable batteries or other rechargeable power sources may includeadditional technical challenges, especially if the device is implanteddeep (e.g., more than three centimeters) within the body of a patient. Arechargeable battery conceptually offers a semi-infinite reservoir ofenergy in which the size of the battery and charged energy densitydetermines the recharge frequency rather than the mission life (underthe assumption of negligible battery capacity fade). A result of asemi-infinite energy source is the opportunity to provide additionalfeatures and functions that may otherwise be limited or unavailablegiven a finite energy source constraint. Another result of thissemi-infinite energy source is the potential reduction or elimination ofa need to perform a surgically invasive device replacement procedurerequired due to exhausting the capacity of the primary (i.e.,non-rechargeable) battery.

In some examples, conventional inductive power transfer to implantedmedical devices may be limited to devices implanted at a depth ofapproximately two inches or less from the surface (e.g., skin) of thepatient. Fast recharge of small, deeply implanted devices such as theMedtronic® Micra™ Pacemaker via transdermal, magnetic induction when thedevice is implanted for example within a chamber of the heart of apatient presents many challenges. These challenges include providing anadequate magnetic field intensity and frequency at the implant locationsuch that rapid recharge can be accomplished without exceeding electricfield and magnetic field exposure safety limits for a patient, whilealso accounting for an uncontrolled orientation of the implanted device,and while accounting for the true spatial location of the device inaddition to the device/antenna orientation.

Further, the exact orientation of the device itself followingimplantation of the device may be unknown, and/or may change after theimplantation procedure. Thus, an implanted medical device that includesa receive antenna, such as a uni-directional or a planar antenna thatmay be sensitive to the alignment of the direction of imposed magneticfield with an orientation of the axis of the antenna, may require moreelaborate procedures and/or more complex recharging equipment for thepurpose of achieving an efficient level of inductive coupling betweenthe magnetic field and the receive antenna. This requirement maynecessitate use of more elaborate alignment procedures to aligndirection of the magnetic field with the orientation of the receiveantenna, or may require use of more complex arrangements of multiplepairs of recharging coils in order to achieve an acceptable level ofinductive coupling efficiency between the magnetic field and the receiveantenna during a recharging procedure.

The devices, systems, and methods described in this disclosure addressmany of the challenges associated with recharging these power sourceswithin implanted medical devices. The systems, devices, and methodsdescribed in this disclosure provide examples of a multi-axis receiveantenna that may be incorporated within an implantable medical device.The multi-axis receive antenna may allow for fast recharge of a batteryor other rechargeable power source within a small, deeply implantedmedical device, such as the Micra™ leadless pacemaker. In some examples,the system for recharging may use a single recharging coil, or in someexamples a single pair of recharging coils, to generate the magneticfield used to recharge the implanted device. The multi-axis receiveantenna may be arranged to generate at least a minimum level ofrecharging current for a given level of power imposed by a magneticfield on the receive antenna regardless of the orientation of themagnetic field relative to an orientation of the implanted device. Theuse of the multi-axis receive antenna may therefore reduce or eliminatethe need for a complex alignment procedure, and/or more complexarrangements of recharging coil(s) in order to achieve a minimum levelof inductive coupling efficiency between the implanted medical deviceand the magnetic field or fields imposed on the device as part of arecharging procedure.

Thus, it is possible to establish a recharging current in the receiveantenna of the implanted medical device that may be independent of theorientation of the recharging magnetic field imposed on the receiveantenna, and thus provides a high level of coupling efficiency betweenthe receive antenna and the magnetic field using just a single rechargecoil, or using just a single pair of recharge coils. The systems,devices, and methods described herein provide a way to allow a magneticfield to efficiently induce electrical energy (e.g., an electricalcurrent) into a receive antenna included within an implanted medicaldevice with a minimum need for complex alignment and orientation betweenwith the receive antenna and the magnetic field. The induced electricalenergy may be used to recharge a power source of the implanted medicaldevice using the externally provided magnetic field, and/or to powerelectronic circuitry included within or coupled to the implanted medicaldevice, including devices that may be considered deeply implanted withinthe patient, (e.g., devices implanted more than two to three centimetersbelow the skin or outer surface of the patient).

The ability to quickly recharge the power source of an implanted medicaldevice, for example within a one hour recharging period of time on amonthly or yearly cycle, without the need to explant the device to doso, allows at least the benefits described above, including use of asmaller power source to help miniaturize the implantable medical deviceitself, and to allow more power, and thus greater functionality for theimplanted medical device by providing an overall longer mission lifespanfor the device using a smaller sized power source. Examples of themulti-axis antenna as described in this disclosure have been shown toprovide recharging currents in devices implanted at about fifteencentimeters within a body of a patient, and to charge a 20 milliamp-hour(mAh) battery of the implanted device in about sixty minutes. Suchexamples include three coils wound on a ferrite core, the core having acubic shape and dimensions of three-millimeters by three-millimeters bythree-millimeters, the magnetic fields having a random orientationrelative to the orientation of the implanted device.

Throughout the disclosure reference is made to a “magnetic field” or to“magnetic fields” in the context of a magnetic field or magnetic fieldsthat is/are generated externally to an implantable medical device, andimposed onto the implanted medical device for the purpose of inducing acurrent into one or more coil windings of a receive antennaconfiguration of the implantable medical device. Examples of waveformsthat may represent one or more parameters of a magnetic field ormagnetic fields are illustrated and described with respect to FIG. 9 .However, the examples of magnetic field(s) are not limited to magneticfields(s) having the particular waveforms illustrated in FIG. 9 . Anymagnetic field or magnetic fields having a parameter (e.g., amplitude orphase) of the magnetic field that varies in time, or that varies in timewith respect to the magnetic field direction of the magnetic field, suchthat a time rate of change of the net magnetic flux intensity imposedonto the coil windings of the receive antenna configuration, and acorresponding change in the electro-motive force (emf) configured togenerate a current or currents in the one or more coil windings iscontemplated by the use of the terms “magnetic field” and “magneticfields” throughout this disclosure.

FIG. 1 is a conceptual drawing illustrating an example medical devicesystem 10 in conjunction with a patient 12 according to various examplesdescribed in this disclosure. The systems, devices, and methodsdescribed in this disclosure may include examples of a multi-axisantenna located within or electrically coupled to an implanted medicaldevice, and provide for charging of these internal, and in someinstances deeply implanted device, such as IMD 15A, IMD 15B, and/orsensor circuits 18, as illustrated and described with respect to FIG. 1. For purposes of this description, knowledge of cardiovascular anatomyis presumed, and details are omitted except to the extent necessary ordesirable to explain the context of the techniques of this disclosure.The systems, devices, and methods described herein may provide efficientcoupling for recharging power sources internal to IMD 15A, IMD 15B,and/or sensor circuits 18, even when these devices are deeply implantedwithin the patient. The implanted devices may include multi-axisantennas that are not necessarily orientation specific with respect tocoupling efficiencies between the antenna of the device beinginductively recharged and the orientation of one or more coils beingused to provide the magnetic field or fields being imposed on the devicefor the purpose of inductively recharging a power source, such as abattery, located within the device. In various examples, IMD 15A and/orIMD 15B may represent examples of a defibrillator, a cardiacresynchronization pacer/defibrillator, or a pacemaker. The medicaldevice system 10 typically includes provisions for interrogating thesedevices through a wireless or other communication protocol using anexternal “instrument” that includes an external-to-the-patient antennaand software/firmware interface to collect data.

In some existing examples of implantable medical devices, techniquesused to keep the size dimensions of the device as small as possibleinclude use of a planar antenna (receiving/transmitting antenna), forexample an antenna comprising a conductive trace printed on a planarsurface such as a substrate, provided within the implantable medicaldevice. One possible advantage of a planar antenna design, as comparedto for example a multi-axis antenna, is that the uni-directional orplanar format of the antenna may take up less space within the device,and may be more easily packaged into the device when size and space areof concern. A disadvantage associated with the planar antenna may bethat coupling efficiencies with respect to receiving power transmittedfrom outside patient to the antenna may be orientation specific. Forexample, the orientation of the electromagnetic and magnetic fieldsbeing imposed on an implanted medical device relative to the orientation(e.g., a normal axis of orientation) of a planar-type receive antennawithin the implanted medical device may have an effect on the efficiencyof transferring power from the electromagnetic and magnetic fields tothe receive antenna.

For some implanted devices, the orientation of the implanted device, andthus the orientation of the receive antenna may not be precisely known,or may shift at some point in time after implantation of the device intoa patient. This shifting of position may include movement of the deviceitself during the time when recharging of the device is being performed.Such shift in position may be caused by motions of tissue in the area ofthe implantation, such as cardiac activity including heartbeats of theheart of the patient, and/or movements of the patient themselves, suchas when the patient is walking, standing, or changing position, such asmovements while lying down. Such changes in orientation of the implantedmedical device may cause issues, including variations in the powertransfer efficiencies, while attempting to inductively recharge a powersource, such as a battery, that is located within the implanted medicaldevice.

Examples of compact multi-axis antennas as described herein may overcomesome or all of these orientation issues related to coupling efficienciesand recharging of an implanted medical device. For example, use of themulti-axis antennas as described in this disclosure within or coupled toan implantable medical device may minimize or even eliminate the issuesrelated to the orientation of the antenna relative to one or morerecharging coils being used to provide the magnetic fields inducingcurrent in the antenna. Because the examples of multi-axis antennas asdescribed in this disclosure are not generally orientation specific, forexample as a planar antenna might be, a recharging process performed onthe implanted medical device having the multi-axis antenna may beperformed by a single planar recharging coil, a simple wound non-planercoil, a helical planer or non-planer, or single pair of rechargingcoils, arranged for example as a Helmholtz coil. A higher level ofcoupling efficiency may be achievable between the recharging coil(s) andthe multi-axis antenna during the recharging process regardless of therelative orientation of the recharging coils relative to themultiple-axis antenna, for example compared to an implanted medicaldevice having a uni-directional antenna and a same relative orientationbetween the uni-directional antenna and the recharging coil(s).

In the illustrated example of FIG. 1 , medical device system 10 includesan implantable medical device (IMD) 15A coupled to a ventricular lead 22and an atrial lead 21. IMD 15A may include an example of a multi-axisantenna as described herein, the multi-axis antenna configured to havecurrents induced into the multi-axis antenna by one or more magneticfields provided externally to the patient 12, the induced current foruse in recharging a power source within IMD 15A. In various examples,IMD 15A is an implantable cardioverter-defibrillator (ICD) capable ofdelivering pacing, cardioversion and defibrillation therapy to the heart13 of a patient 12. Ventricular lead 22 and atrial lead 21 areelectrically coupled to IMD 15A, and extend into the heart 13 of patient12. Ventricular lead 22 includes electrodes (not labeled in FIG. 1 )positioned on the lead in the patient's right ventricle (RV) for sensingventricular EGM signals and pacing in the RV. Atrial lead 21 includeselectrodes (not labeled in FIG. 1 ) positioned on the lead in the rightatrium (RA) of patient 12 for sensing atrial EGM signals and pacing inthe RA. Ventricular lead 22 and/or atrial lead 21 may also include coilelectrodes used to deliver cardioversion and defibrillation shocks. Theterm “anti-tachyarrhythmia shock” may be used herein to refer to bothcardioversion shocks and defibrillation shocks. IMD 15A may use bothventricular lead 22 and atrial lead 21 to acquire cardiac electrogram(EGM) signals from patient 12 and to deliver therapy in response to theacquired data. Medical device system 10 is shown as having a dualchamber IMD configuration, but other examples may include one or moreadditional leads, such as a coronary sinus lead extending into the rightatrium, through the coronary sinus and into a cardiac vein to positionelectrodes along the left ventricle (LV) for sensing LV EGM signals anddelivering pacing pulses to the LV. In other examples, a medical devicesystem may be a single chamber system, or otherwise not include atriallead 21.

Processing circuitry, sensing circuitry, a multi-axis antenna, arechargeable power source, and other circuitry configured for performingthe techniques described herein or otherwise ascribed to IMD 15A may behoused within a sealed housing 23. Housing 23 (or a portion thereof) maybe conductive so as to serve as an electrode for pacing or sensing, oras an active electrode during defibrillation. As such, housing 23 isalso referred to herein as “housing electrode” 23. Housing 23 mayinclude one or more electrodes with a high-capacitance portion and alow-capacitance portion. The high-capacitance portion and thelow-capacitance portion may be formed using two different materials.

IMD 15A may transmit EGM signal data and cardiac rhythm episode data, aswell as data regarding delivery of therapy by IMD 15A, to an externaldevice 11. External device 11 may also be referred to as an“instrument,” which may include any of the devices described throughoutthe disclosure as devices located externally to the patient, and in someexamples may be included as part of a recharging system configured torecharge the battery or other power source provided within IMD 15A. Forexample, external device 11 as illustrated in FIG. 1 may be a computingdevice, e.g., used in a home, ambulatory, clinic, or hospital setting,to communicate with IMD 15A via wireless telemetry. External device 11may be coupled to a remote patient monitoring system, such as Carelink®,available from Medtronic plc, of Dublin, Ireland. External device 11 maybe, as examples, a programmer, external monitor, or consumer device,e.g., a smart phone.

External device 11 may be used to program commands or operatingparameters into IMD 15A for controlling its functioning, e.g., whenconfigured as a programmer for IMD 15A. External device 11 may be usedto interrogate IMD 15A to retrieve data, including device operationaldata as well as physiological data accumulated in IMD 15A memory. Theinterrogation may be automatic, e.g., per a schedule, or in response toa remote or local user command. Examples of communication techniquesused by IMD 15A and external device 11 may include tissue conductancecommunication (TCC) and/or radio frequency (RF) telemetry, which may bean RF link established via Bluetooth®, WiFi, or medical implantcommunication service (MICS).

As illustrated in FIG. 1 the medical device system 10 may also includean intracardiac pacing device IMD 15B. IMD 15B may include an example ofa multi-axis antenna as described herein, the multi-axis antennaconfigured to have currents induced into the multi-axis antenna by oneor more magnetic fields provided externally to the patient 12, theinduced currents for use in recharging a power source within IMD 15B. Inthe illustrated example, IMD 15B is implanted in the right ventricle ofpatient 12, e.g., internal to the heart 13 of patient 12. In someexamples, one or more IMDs like IMD 15B (not shown in FIG. 1 ) mayadditionally or alternatively be implanted within other chambers ofheart 13, or attached to the heart epicardially. IMD 15B may beconfigured to sense electrical activity of heart 13 and deliver pacingtherapy, e.g., bradycardia pacing therapy, cardiac resynchronizationtherapy (CRT), anti-tachycardia pacing (ATP) therapy, and/or post-shockpacing to heart 13. IMD 15B may be attached to an interior wall of heart13 via one or more fixation elements (not shown in FIG. 1 ), thatpenetrate the cardiac tissue. These fixation elements may secure IMD 15Bto the cardiac tissue and retain an electrode (e.g., a cathode or ananode) on the housing of IMD 15B in contact with the cardiac tissue. Inaddition to delivering pacing pulses, IMD 15B may be capable of sensingelectrical signals using the electrodes carried on the housing of IMD15B. These electrical signals may be electrical signals generated bycardiac muscle and indicative of depolarizations and repolarizations ofheart 13 at various times during the cardiac cycles of heart 13.

In some examples, IMD 15A and IMD 15B may both be configured to deliverpacing therapy. In such examples, IMD 15A and IMD 15B may deliverypacing therapy to the right and/or left ventricles of heart 13,respectively, to provide CRT pacing. Additionally, IMD 15A and IMD 15Bmay both be configured to detect tachyarrhythmias, and deliveranti-tachyarrhythmia therapy. IMD 15A and IMD 15B may be configured tocoordinate their cardiac rhythm detection and treatment activities. Insome examples, IMD 15A and IMD 15B may engage in wireless communicationbetween IMD 15A and IMD 15B to facilitate such coordinated activity. Thewireless communication may by via TCC, and may be one-way communicationin which one device is configured to transmit communication messages andthe other device is configured to receive those messages, or two-waycommunication in which each device is configured to transmit and receivecommunication messages.

In various examples, IMD 15B is configured to wirelessly communicatedirectly with external device 11, using any of the communicationprotocols described above with respect to IMD 15A. External device 11may be, as examples, a programmer, external monitor, or consumer device,e.g., a smart phone, that may be used to program commands or operatingparameters into IMD 15B for controlling the functioning of the device.External device 11 may be used to interrogate IMD 15B to retrieve data,including device operational data as well as physiological orneurological data accumulated in memory of IMD 15B. The interrogationmay be automatic, e.g., according to a schedule, or in response to aremote or local user command. In some examples, communication betweenIMD 15B and external device 11 may take place through IMD 15A, whereinIMD 15B communications with IMD 15A, and IMD 15A communicates withexternal device 11. Examples of communication techniques used by IMD 15Aand/or 15B and external device 11 are not limited to any particularcommunication technique or communication protocol, and in some examplesTCC or RF telemetry, which may be an RF link established via Bluetooth®,WiFi, or medical implant communication service (MICS).

In various examples, communications provided from IMD 15A and/or IMD 15Bmay include data and/or other information related to the inductivecharging of these devices. For example, when an electromagnetic ormagnetic field is imposed on IMD 15A and/or IMD 15B for the purpose ofinductively charging these device(s), information related to thecoupling efficiency of inductive coupling to the device, and/or forexample the state of charge (e.g., percent of charge relative to a fullcharge) may be transmitted from one or both of IMD 15A and/or IMD 15B toexternal device 11 as part of the recharging process. Other information,such as time to full charge, rate of recharge, and temperature of thedevice may also be provided as transmitted information from thedevice(s) being recharged. In some examples, this information may beused to adjust parameters, such as the field strength of the fields usedto induce the energy in the antenna for recharging of IMD 15A and/or IMD15B, or for example to provide information used to reconfigure theelectrical parameters being used to energize the coil or coils that areproviding the fields used for the inductively coupled recharging ofthese device(s).

In addition, information may be provided by IMD 15A and/or IMD 15B thatis indicative of the level of the recharging of one or both of IMD 15Aand/or IMD 15B that has been achieved or completed, which may then beused to determine when to further regulate, stop, or otherwise terminatethe recharging process. For example, during the recharging process IMD15A and/or IMD 15B may transmit data or other information indicatingthat the device, respectively, is fully recharged. The indication maythen be used by the external devices providing the fields (not show inFIG. 1 ) to stop the charging process, which may include removing thefields used to recharge IMD 15A and/or IMD 15B from being imposed onthese devices. In addition, monitoring the temperature of these devicesmay be important, as overheating of an implanted device as a result ofthe recharging process may damage the device, or present a safety issuefor the patient. Adjustments to the intensities of the fields beingimposed on the device(s), and/or termination of the recharging processaltogether may be made based on the monitored temperature of the devicebeing recharged as a part of the recharging process.

In various examples, one or more additional sensor circuits may belocated outside of or separately located relative to the IMD 15A and/orIMD 15B. These one or more additional sensor circuits are illustrativelyrepresented by sensor circuits 18. Sensor circuits 18 may include asingle sensor circuit configured to sense a particular physiological orneurological parameter associated with patient 12, or may comprise aplurality of sensor circuits, which may be located at various and/ordifferent positions relative to patient 12 and/or relative to eachother, and may be configured to sense one or more physiologicalparameters associated with patient 12.

For example, sensor circuits 18 may include a sensor operable to sense abody temperature of patient 12 in a location of the sensor circuits 18,or at the location of the patient where a temperature sensor coupled bya lead to sensor circuits 18 is located. In another example, sensorcircuits 18 may include a sensor configured to sense motion, such assteps taken by patient 12 and/or a position or a change of posture ofpatient 12. In various examples, sensor circuits 18 may include a sensorthat is configured to detect breaths taken by patient 12. In variousexamples, sensor circuits 18 may include a sensor configured to detectheartbeats of patient 12. In various examples, sensor circuits 18 mayinclude a sensor that is configured to measure systemic blood pressureof patient 12.

In some examples, one or more of the sensors comprising sensor circuits18 may be implanted within patient 12, that is, implanted below at leastthe skin level of the patient. In some examples, one or more of thesensors of sensor circuits 18 may be located externally to patient 12,for example as part of a cuff or as a wearable device, such as a deviceimbedded in clothing that is worn by patient 12. In various examples,sensor circuits 18 may be configured to sense one or more physiologicalparameters associated with patient 12, and to transmit datacorresponding to the sensed physiological parameter or parameters to IMD15A, as represented by the lightning bolt coupling sensor circuits 18 toIMD 15A. Transmission of data from sensor circuits 18 to IMD 15A invarious examples may be performed via wireless transmission, using forexample any of the formats for wireless communication described above.In various examples, transmission of data from one or more of thesensors comprising sensor circuits 18 to IMD 15A may be performed by awired connection between the sensor circuits 18 and IMD 15A. When sensorcircuits 18 are implanted devices that are implanted within patient 12,one or more of the sensor circuits may include any examples of themulti-axis antenna described in this disclosure, and the rechargingtechniques as described throughout this disclosure may be used to alsorecharge a power source, such as a battery, located within the implantedsensor(s) that is configured to provide power to operate the sensor.

In various examples, IMD 15A and or IMD 15B may communicate wirelesslyto an external device (e.g., an instrument or instruments) other than orin addition to external device 11, such as transceiver 16 shown in FIG.1 . In various examples, transceiver 16 as shown in FIG. 1 is an accesspoint, such as access point 145 illustrated and described with respectto FIG. 7 , that provides a wireless communication link between IMD 15Aand/or IMD 15B, and a network such as network 147 illustrated anddescribed with respect to FIG. 7 . In various examples, transceiver 16is communication circuitry 224 of recharging system 200 shown in FIG. 8, wherein communication circuitry 224 is configured to communicate withIMD 15A and/or IMD 15B during the recharging process of these devices,as further described below. Examples of communication techniques used byany of the devices described above with respect to FIG. 1 andtransceiver 16 may include radiofrequency (RF) telemetry, which may bean RF link established via Bluetooth®, WiFi, or medical implantcommunication service (MICS).

For the remainder of the disclosure, a general reference to a medicaldevice system may refer collectively to include any examples of medicaldevice system 10, a general reference to IMD 15 may refer collectivelyto include any examples of IMD 15A and/or IMD 15B, a general referenceto sensor circuits may refer collectively to include any examples ofsensor circuits 18, a general reference to external device may refercollectively to include any examples of external devices 11, and ageneral reference to a transceiver may refer collectively to anyexamples of transceiver 16.

FIG. 2 is a conceptual drawing illustrating an example configuration ofan implantable medical device 30 according to various examples describedin this disclosure. Device 30 in some examples is an intracardiac pacingdevice designed to be implanted within a chamber of the heart of apatient. Device 30 in some examples is IMD 15B as illustrated anddescribed with respect to FIG. 1 . Device 30 may be configured to beimplanted in the right ventricle of the heart of a patient, as depictedin FIG. 1 , or in some other chamber of the heart of a patient. As shownand described with respect to FIG. 2 , device 30 may be an example of animplantable medical device that includes a multi-axis antenna 40 thatmay be used to provide a recharging current that is induced into thecoils of the multi-axis antenna for the purpose of recharging a powersource, such as battery 39, within device 30. In some examples, device30 is a Medtronic® Micra™ Transcatheter Pacing System developed byMedtronic, plc, of Dublin, Ireland.

As shown in FIG. 2 , device 30 includes first housing portion 31, anantenna window 42, a second housing portion 36, and an end cap 34coupled together to form the external portions of device 30. Firsthousing portion 31, antenna window 42, second housing portion 36, andend cap 34 may be “sealingly joined” together as shown in FIG. 2 to forma hermetically sealed housing that encloses a battery 39, a multi-axisantenna 40, and electronic circuitry 45 of device 30. As used herein,“sealingly coupled” or “sealingly joined” refers to two or moreindividual pieces of material that are mechanically coupled to oneanother at a joint or along a seam that is formed to provide a hermeticseal at the joint or seam between the two or more pieces. Device 30 asshown in FIG. 2 may further includes electrode 32, electrode 33,fixation mechanisms 35, and flange 38 including an opening 37. Bothfirst housing portion 31, second housing portion 36, and end cap 34 maybe formed from electrically insulating material, and/or may be coatedwith a polymer material such as a poly-para-xylylene (commonly“Parylene”). In some examples, one or both of first housing portion 31and second housing portion 36 may be formed of same material includingtitanium. In some examples, end cap 34 may be formed in whole or in partfrom an electrically insulative material, such as a plastic material.

Although device 30 is generally described as including one or moreelectrodes, device 30 may typically include at least two electrodes(e.g., electrodes 32 and 33) to deliver an electrical signal (e.g.,therapy such as cardiac pacing) and/or provide at least one sensingvector. Electrode 32 is carried on the portion device 30 indicated asfirst housing portion 31, and electrode 33 is carried at the upper ordistal portion of end cap 34. Electrodes 32 and 33 may be consideredleadless electrodes in the sense that they are not coupled to device 30or a housing portion of device 30 by a lead. In the example of FIG. 2 ,electrode 32 may be a ring or cylindrical electrode disposed on theexterior surface of first housing portion 31, and electrode 33 may bedisposed on the exterior surface of end cap 34. Electrode 33 may be acircular electrode positioned to contact cardiac tissue uponimplantation of device 30. Electrode 33 may be used as a cathode andelectrode 32 may be used as an anode, or vice versa, for deliveringcardiac pacing such as bradycardia pacing, cardiac resynchronizationtherapy (CRT), antiachycardia pacing (ATP), or post-shock pacing.However, electrodes 32 and 33 may be used in any stimulationconfiguration. In addition, electrodes 32 and 33 may be used to detectintrinsic electrical signals from cardiac muscle tissue. Electrode 33may be configured to contact cardiac tissue such as an interior wall ofthe right ventricle, when device 30 is implanted with the heart of apatient.

Fixation mechanisms 35 may be arranged to attach device 30 to cardiactissue. Fixation mechanisms 35 may be active fixation tines, screws,clamps, adhesive members, or any other mechanisms for attaching a deviceto tissue. As shown in the example of FIG. 2 , fixation mechanisms 35may be constructed of a memory material, such as a shape memory alloy(e.g., nickel titanium), that retains a preformed shape. Duringimplantation, fixation mechanisms 35 may be flexed forward to piercetissue, and then allowed to flex back towards second housing portion 36.In this manner, fixation mechanisms 35 may be embedded within the targettissue to secure device 30 in place relative to the target tissue. Aflange 38 may be provided on one end of device 30, for example extendingfrom first housing portion 31, to enable tethering and/or extraction ofdevice 30. For example, a suture or other device may be inserted aroundflange 38 and/or through opening 37 and attached to tissue. In thismanner, flange 38 may provide a secondary attachment structure to tetheror retain device 30, for example within the heart. Flange 38 and/oropening 37 may also be used to extract device 30 once the device needsto be explanted (or removed) from the patient if such action is deemednecessary.

Electronic circuitry 45, including communication and/or rechargingcircuitry coupled to the multi-axis antenna 40, and a power source suchas battery 39, may be housed within the housing of device 30. The powersource is not limited to any particular type of power source, and insome examples, is a rechargeable battery, which is coupled to theelectronic circuitry 45 and is configured to provide electrical power tothe electronic circuitry. The electronic circuitry 45 of device 30 isnot limited to any particular type or arrangement of electronic devices,and may include any type(s) of devices arranged to perform any of thefunctions ascribed to device 30. For example, electronic circuitry 45may include electronic devices configured to perform any of the patientmonitoring functions and/or to provide electrical stimulation therapythrough the electrodes (e.g., electrodes 32 and 33) of device 30.Electronic circuitry 45 may further include communication circuitryconfigured to provide wireless communication between device 30 and otherdevices, such as external device 11 and/or transceiver 16 as illustratedand described above for example with respect to FIG. 1 . Thecommunication circuitry of device 30 may utilize the multi-axis antenna40 for transmission of signals transmitted from device 30, and forreception of signals transmitted to device 30 from one or more devicesexternal to device 30.

In addition, multi-axis antenna 40 may be configured to receiveelectrical energy imposed on device 30 in the form of one or moremagnetic fields, and to recharge battery 39 using energy inductivelycoupled to antenna 40 from these field(s), which may also be referred toas wireless power transfer. In order to achieve a high level of couplingefficiency between the antenna 40 and the magnetic field(s) beingimposed on device 30 for the purpose of recharging battery 39, antenna40 is arranged as a multi-axis antenna, for example including a firstcoil, a second coil and a third coil (not specifically shown in FIG. 2 ,but for example first coil 71, second coil 76, and third coil 80 asillustrated and described with respect to FIG. 4 ). As shown in FIG. 2 ,the multi-axis antenna 40 is positioned within device 30, for examplerelative to longitudinal axis 46 of device 30, to align with and in someexamples be encircled by antenna window 42.

As further described below, the antenna window 42 may be formed of amaterial, for example a material having a high value relative toelectrical resistivity, that allows for transmission of theelectromagnetic energy being imposed onto device 30 for rechargingpurposes to penetrate and pass through the antenna window 42, and reachthe antenna 40. The antenna window 42 may be referred to as being formedfrom a “radio transmissive” material that also provides a low relativedielectric constant (i.e., high relative electrical resistivity), andlow magnetic permeability. Electrical resistivity may be represented bythe Greek letter ρ (rho), and in International System (SI) units ismeasured in ohm-meter (Ω·m), and which may vary for a given materialbased on temperature. An example of a material, such as certain metals,that may be considered to be a good electrical conductor and thus have alow value for electrical resistivity, is copper, having a ρ value ofapproximately 1.68×10⁻⁸ Ω·m at 20 degrees Celsius (° C.). An example ofa material that may be considered to be poor conductors of electricity,e.g., and electrical insulator, and thus having a high value for ρ mayinclude glass, which can have a ρ value in a range of 10×10¹⁰ to 10×10¹⁴Ω·m at 20° C. Another example of a material having a high value for ρ issapphire, which in some examples has a ρ value of 10¹⁴ Ω/centimeter at23° C.

In order to allow higher frequency magnetic fields to penetrate thehousing of device 30 and reach antenna 40, at least the antenna window42 portion of the device may be formed of a material, such as sapphire,that has a high value for electrical resistivity, at least attemperatures normally experienced by devices after being implantedwithin a patient, (e.g., temperatures normally not to exceed 39 to 40°C. on the exterior surface of the implanted device even for a briefperiod of time, such as when the device is being recharged. To allow useof higher frequency magnetic fields for the purpose of recharging device30, antenna window 42 may be made of a radio transparent material havinghigh electrical resistivity (e.g., in a range of 1×10¹¹ to 1×10¹⁶Ohms/centimeter) and a low magnetic permeability. A wide range ofmaterials will satisfy these requirements, examples such as sapphire, aglass material, or polymeric materials are typically employed having adielectric constant ranging from about 1 to 12, Use of sapphire or aglass material for antenna window 42 may allow a higher frequency of aninduced magnetic field to be transmitted through the antenna window 42and be imposed on antenna 40 relative to other materials that may notprovide a same level, or as high a value, for electrical resistivity.For example, by using an antenna window 42 made from sapphire, magneticfields having frequencies ranging from about 100 KHz to 10 MHz beimposed on device 30, wherein the sapphire allows the imposed magneticfield or fields to pass through the antenna window 42 and induce acurrent in one or more of the coils forming multi-axis antenna 40. Theability to use higher frequency magnetic fields allows for more energy,and thus a larger current, to be induced into the coil or coils ofantenna 40 at any given time, or over a particular time period duringwhich the higher frequencies are being imposed on device 30, as comparedto using a lower frequency magnetic field. Antenna window 42 is notlimited to being formed from a visually transparent material. Examplesof material used to form antenna window 42 may include any type ofmaterial having a minimum value for electrical resistivity (e.g., a goodelectrical insulator with low dielectric constant value) and lowmagnetic permeability, and that meets other manufacturing requirementsand complies with any other applicable regulatory requirements, such asbiocompatibility requirements, for use in implantable medical devices.

As illustrated in FIG. 2 , first housing portion 31 is sealingly coupledto antenna window 42 at a first seam 43. The antenna window 42 issealingly coupled to the second housing portion 36 of device 30 atsecond seam 44. Antenna 40 may be positioned within the portion ofdevice 30 that is encircled by the antenna window 42. The electroniccircuitry 45 may be positioned within the portion of device 30 encircledby second housing portion 36. End cap 34 may be sealingly coupled to theend of second housing portion 36 that is opposite the end of secondhousing portion 36 coupled to the antenna window 42.

Examples of antenna window 42 are not limited to being formed from amaterial that is different from the first housing portion 31 and/ordifferent from the second housing portion 36. In some examples, theantenna window 42 and the second housing portion 36 may be formed of asame material, such as sapphire, that is a different material used toform the first housing portion 31. In some examples, the first housingportion 31, the antenna window 42, and the second housing portion 36 areall formed of a same material, such as titanium or a titanium alloy, andmay be formed as a single piece, or as separate pieces sealingly joinedtogether.

Because antenna 40 is arranged as a multi-axis antenna, the direction,e.g., the orientation of the imposed magnetic field or magnetic fieldsreaching antenna 40 may provide a minimum level of coupling efficientlybetween the antenna and the field(s) regardless of the relativeorientation of device 30 and the direction of orientation of the imposedmagnetic field(s). In order words, the antenna 40 itself may not beorientation specific with respect to the orientation of antenna 40relative to the orientation of the fields imposed on device 30 for thepurpose of inductive power transfer that can be used for recharging ofbattery 39. For example, any angle of direction for a magnetic fieldimposed on device 30 may induce some level of current within antenna 40for a given level of the magnetic field strength imposed on device 30and thus on antenna 40. The specific angle of the direction of theactual magnetic field in some examples of devices may be irrelevant withrespect to the level of current induced in antenna 40 for a given levelof energy of the magnetic field or fields.

In some examples, various other aspects of the device 30 itself, such asinterference with the transmission of the magnetic field created byfirst housing portion 31, and/or second housing portion 36, or forexample by materials used to form certain portion of device 30 (e.g., atitanium material used to form a cover for battery 39), may result in alower level of induced currents when the magnetic fields are imposed atcertain angles relative to the device compared to other angles forimposing the magnetic field onto the device. For devices where certainangles of the direction of the actual magnetic field being imposed onthe device may incur interference with the inductive coupling of themagnetic field with the multi-axis antenna of the device, some level ofcurrent or currents may still be induced into the multi-axis antenna,but may for example provide a lower level of induced current compared toother angles of direction of the actual magnetic field that may be usedto impose the magnetic field onto the multi-axis antenna. In suchinstances, a feedback signal provided by the device having themulti-axis antenna and that is indicative of the level of inducedcurrent(s) being generated by the multi-axis antenna may be used toreorient the direction of the magnetic fields relative to the device.Based on monitoring the feedback signal, a different relative anglebetween the device and the direction of the magnetic fields can bearranged, for example by moving the position of the transmit coil(s)providing the magnetic field, and thus may provide a better level ofinductive coupling between the magnetic field and the multi-axisantenna.

Based on the capability of multi-axis antenna 40 to provide at least aminimum level of induced current from the antenna for a given powerlevel of a magnetic field being imposed onto the antenna regardless ofthe angle of incidence (orientation) of the magnetic field relative tothe antenna within the bounds determined by other physical factorsrelated to the device itself, a specific orientation between antenna 40and the direction of the incident magnetic field imposed on antenna 40is not required. The minimum current level may be induced into one ormore of the coils of multi-axis antenna 40 regardless of the specificorientation of the incident magnetic field and the relative orientationof the multi-axis antenna to those magnetic field(s). This feature isuseful when performing a recharging operation on an implanted devicethat includes a multi-axis antenna within the device because a minimumlevel of recharging current can be induced into the antenna of thedevice without the need for an elaborate or complex alignment procedureto orient the magnetic fields to a particular orientation of the deviceand the antenna. For deeply implanted devices whose exact orientationmay not be known, or whose position may have shifted, or may actually beshifting during a recharging session of the device, the feature of nothaving to determine this relative orientation may allow less expensive,less complicated, and less time-consuming techniques to be used toefficiently recharging the power source located within the implanteddevice.

While examples of induced current as described above have been describedwith respect to recharging a power source located within the device, themulti-axis antenna and features of inductive power transfer to thedevice through current induced in the multi-axis antenna may also beapplied when inducing a current into the antenna for the purpose ofproviding electrical energy to directly power the operation of thedevice itself, for example in a passive device that may only operatewhen powered by external power source.

As shown in FIG. 2 , power source (battery) 39 is comprises some portionof the device such as first housing portion 31, antenna 40 is locatedwithin an interior space encircled by antenna window 42, and electroniccircuitry 45 is located substantially within the interior space ofdevice 30 formed by second housing portion 36. Examples of thearrangement of the devices within the housing of device 30 are notlimited to the arrangement as shown in FIG. 2 , and other arrangementsof the devices and components included within device 30 are contemplatedfor use with the multi-axis antenna described in this disclosure. Forexample, as shown in FIG. 2 antenna 40 is arranged on a substrate orother planar surface, which in some examples is a circuit board 41.Electrical conductors may extend from circuit board 41 and beelectrically coupled to the electronic circuitry 45, and/or to one ormore terminals of battery 39. In other examples, antenna 40 isphysically coupled to a separate circuit board such as circuit board 41.In some examples, portions of circuit board 41 may be formed as part ofa larger circuit board, or as a substrate that may also include otherelectrical devices, such as electrical devices utilized as part of therecharging circuitry of device 30 and/or electrical devices ofelectronic circuitry 45.

In some examples of device 30, first housing portion 31, antenna window42, and second housing portion 36 may not be separately formed pieces,but instead may be one piece formed from a same type of material, andsealingly coupled to end cap 34 to form the hermitically sealed housingfor device 30. In such examples, antenna window 42 is not provided as aseparate piece of material, and instead is considered to be formed ofthe same material forming the one piece of material forming the housingportions of device 30. Device 30 is not limited to a device having anyparticular shaped housing. As shown in FIG. 2 , device 30 has agenerally circular cross-sectional shape along longitudinal axis 46 forany plane that is perpendicular to longitudinal axis 46 throughout thefirst housing portion 31, antenna window 42, and second housing portion36. In some examples, the circular cross-sectional shape of device has adiameter of approximately six millimeters. However, device 30 is notlimited to having a circular cross-sectional shape as described above,and portions of device 30 may have other shapes in cross-sectionrelative to longitudinal axis 46, including a rounded square, a roundedrectangle, or an elliptical shape. Additional examples of multi-axisantenna that may be provided as antenna 40 in device 30 and systems andtechniques to recharge device 30 are illustrated and described belowwith respect to FIGS. 3-11 .

FIG. 3 illustrates a schematic diagram 50 including a three-axis antenna63 coupled to a rechargeable power source 62 of an implantable medicaldevice according to various examples described in this disclosure. Thethree-axis antenna 63 and/or the additional circuitry illustrated inFIG. 3 may be representative of a multi-axis antenna that is includedwithin or may be coupled to an implantable medical device such as IMD15A or IMD 15B as shown in FIG. 1 , or device 30 as shown in FIG. 2 . Asshown in FIG. 3 , antenna 63 includes a first coil 52, a second coil 55,and a third coil 58, each coil formed in conjunction with a ferrite core51 common to all three coils.

First coil 52 may be formed as a winding encircling a portion of ferritecore 51. First coil 52 may be wound from an electrical conductor, suchas a conductive wire, that is wound around ferrite core 51 so that amagnetic field imposed on the antenna 63 having a magnetic fielddirection that is colinear with the X-axis of the three-axis coordinatesystem 64 provides a maximum level of coupling efficiency between themagnetic field and the first coil 52. First coil 52 may therefore alsobe referred to as the X-axis coil, and considered to have an axis oforientation, (e.g., a normal axis) that aligns with the X-axis ofthree-axis coordinate system 64.

Second coil 55 of antenna 63 may be wound from a separate electricalconductor relative to the electrical conductor used to form the firstcoil 52. The electrical conductor used to form the second coil 55 may bea same type of electrical conductor, such as a same type of conductivewire, as used to form the first coil 52. The electrical conductor ofsecond coil 55 may be wound around ferrite core 51 so that that amagnetic field imposed on the antenna 63 having a magnetic fielddirection that is colinear with the Y-axis of the three-axis coordinatesystem 64 provides a maximum level of coupling efficiency between themagnetic field and the second coil 55. Second coil 55 may therefore alsobe referred to as the Y-axis coil, and considered to have an axis oforientation, (e.g., a normal axis) that aligns with the Y-axis ofthree-axis coordinate system 64.

Third coil 58 of antenna 63 may be wound from a separate electricalconductor relative to the electrical conductors used to form the firstcoil 52 and the second coil 55. The electrical conductor used to formthe third coil 58 may be a same type of electrical conductor, such as asame type of conductive wire, used to form the first coil 52 and thesecond coil 55. The electrical conductor of third coil 58 may be woundaround ferrite core 51 so that that a magnetic field imposed on theantenna 63 having a magnetic field direction that is colinear with theZ-axis of the three-axis coordinate system 64 provides a maximum levelof coupling efficiency between the magnetic field and the third coil 58.Third coil 58 may therefore also be referred to as the Z-axis coil, andconsidered to have an axis of orientation, (e.g., a normal axis) thataligns with the Z-axis of three-axis coordinate system 64.

The relative physical arrangement and orientation of each of the firstcoil 52, the second coil 55, and the third coil 58 may be such that amagnetic field imposed on these coils at some angle that is notnecessarily colinear with the corresponding X, Y, or Z-axis (and thusnot necessarily providing maximum coupling efficiency for any given oneof the coil), may still generate an induced current in one, two, or allthree of these coils. The sum of these induced currents may be at leastequal to a minimum level of current that would be induced in any one ofthese coils in instances where the direction of the magnetic fieldimposed on the coils is colinear with one of the X, Y, or Z-axis ofcoordinate system 64. As such, the particular orientation of antenna 63may become irrelevant relative to the orientation of the magnetic fieldimposed on the antenna for the purpose of inducing at least a minimumlevel of current, for example a recharging current, into antenna 63 fora given magnetic field having a given field strength.

As shown in FIG. 3 , a capacitor 53 is coupled in parallel with thefirst coil 52. Capacitor 53 may be sized with respect to a capacitancevalue so that in conjunction with first coil 52, a tank circuit isformed having a resonant frequency that matches a frequency that may beapplied by externally generated magnetic field(s) imposed onto firstcoil 52 for the purpose of inducing a current into first coil 52. Havingthe tank circuit comprising first coil 52 and capacitor 53 tuned to havea resonate frequency that matches a frequency of the magnetic field(s)intended to be imposed onto the first coil 52 allows a higher level ofcoupling efficiency to be achieved between the imposed magnetic field(s)and the first coil 52 compared to other frequencies that are not matchedto the resonate frequency of the tank circuit. A diode 54 is coupled inseries with a first end of first coil 52 and a terminal of the capacitor53. A second end of first coil 52 is coupled to a common voltage node68. Diode 54 in some examples is a Schottky diode. Diode 54 isconfigured to rectify any current flows induced in first coil 52 so thatall current flows generated in the first coil 52 as a result ofexternally imposed magnetic field(s) will flow through diode 54 in thedirection indicated as “I(x),” and toward node 65. In some examples, aminimum level of voltage is required to forward bias diode 54, andtherefore no current will be provided as current flow I(x) until theminimum voltage level required to forward bias diode 54 is present,resulting in a minimum initial level of current flow being provided bythe current induced into first coil 52.

Similarly, a capacitor 56 may be coupled in parallel with the secondcoil 55. Capacitor 56 may be sized with respect to a capacitance valueso that in conjunction with second coil 55, a tank circuit is formedhaving a resonant frequency that matches an intended frequency that maybe applied by externally generated magnetic field(s) imposed onto secondcoil 55 for the purpose of inducing a current into second coil 55. Thetank circuit comprising second coil 55 and capacitor 56 may be tuned tohave a resonate frequency that matches the frequency of the magneticfield(s) intended to be imposed onto the second coil 55 to provide ahigher level of inductive coupling efficiency as described above withrespect to first coil 52. A diode 57 is coupled in series with a firstend of second coil 55 and a terminal of the capacitor 56. A second endof second coil 55 is coupled to the common voltage node 68. Diode 57 insome examples is a Schottky diode. Diode 57 is configured to rectify anycurrent flows induced in second coil 55 so that all current flowsgenerated in the second coil 55 as a result of externally imposedmagnetic field(s) will flow through diode 57 in the direction indicatedas “I(y),” and toward node 66. In some examples, a minimum level ofvoltage is required to forward bias diode 57, and therefore no currentwill be provided as current flow I(y) until the minimum voltage levelrequired to forward bias diode 57 is present, resulting in a minimuminitial level of current flow being provided by the current induced intosecond coil 55.

As illustrated in schematic diagram 50, a capacitor 59 is coupled inparallel with the third coil 58. Capacitor 59 may be sized with respectto a capacitance value so that in conjunction with third coil 58, a tankcircuit is formed having a resonant frequency that matches an intendedfrequency that may be applied by externally generated magnetic field(s)imposed onto third coil 58 for the purpose of inducing a current intothird coil 58. The tank circuit comprising third coil 58 and capacitor59 may be tuned to have a resonate frequency that matches the frequencyof the magnetic field(s) intended to be imposed onto the third coil 58to provide a higher level of inductive coupling efficiency as describedabove with respect to first coil 52 and second coil 55. A diode 60 iscoupled in series with a first end of third coil 58 and a terminal ofthe capacitor 59. A second end of third coil 58 is coupled to the commonvoltage node 68. Diode 60 in some examples is a Schottky diode. Diode 60is configured to rectify any current flows induced in third coil 58 sothat all current flows generated in the third coil 58 as a result ofexternally imposed magnetic field(s) will flow through diode 60 in thedirection indicated as “I(z),” and toward node 67. In some examples, aminimum level of voltage is required to forward bias diode 60, andtherefore no current will be provided as current flow I(z) until theminimum voltage level required to forward bias diode 60 is present,resulting in a minimum initial level of current flow being provided bythe current induced into third coil 58.

In addition to rectifying current, diodes 54, 57, and 60 also preventcurrent flows from one of coils 52, 55, and 58 from being backwarddriven into another one of the coils. For example, diode 54, by havingthe cathode of the diode coupled to node 65, will block any I(y) currentprovided by second coil 55, and any I(z) current provided by third coil58, from being driven through first coil 52. Diode 57, by having thecathode of the diode coupled to node 66, will block any I(x) currentprovided by first coil 52, and any I(z) current provided by third coil58, from being driven through second coil 55. Diode 60, by having thecathode of the diode coupled to node 67, will block any I(x) currentprovided by first coil 52, and any I(y) current provided by second coil55, from being driven through third coil 58. As a result, any currentsprovided by first coil 52 as current I(x), will be summed together withany currents provided by second coil 55 as current I(y) and any currentsprovided by third coil 58 as current I(z). The sum of currents I(x),I(y), and I(z) will be provided at node 67.

A smoothing capacitor 61 may be coupled between node 67 and the commonvoltage node 68 to smooth out any rapid variations in the currentprovided to node 67. In addition, a power source 62 is coupled to node67 through switching device 92. Switching device 92 is not limited toany particular type of device, and in some examples, may be asemiconductor device, such as a transistor, that is controlled byrecharging circuitry 90. When switching device is operated to couplenode 67 to power source 62 as shown in FIG. 3 , current flows providedas current flows I(x), I(y), and I(z) may be provided to a firstterminal of power source 62 through switching device 92 from node 67. Asecond terminal of power source 62 is coupled to the common voltage node68. When coupled to node 67, a flow of current from node 67 may beprovided as current I(x,y,z) at the first terminal of power source 62,and provide a source of electrical energy to recharge power source 62.In various examples, recharging circuitry 90 is configured to controlthe coupling of node 67 to power source 62 by controlling switchingdevice 92, and thus regulate and control the rate and intervals duringwhich power source 62 receives the current flow from node 67.

Recharging circuitry 90 may include sensing circuitry 91. Sensingcircuitry 91 may include sensors and sensor processing circuitry (notshown in FIG. 3 ) configured for example to sense one or more parametersassociated with the operation of the devices illustrated in FIG. 3 . Forexample, sensing circuitry 91 may include one or more sensors configuredto sense a level of current flow being provided by one or more of coils52, 55, and 58 as current I(z), I(y), and/or I(z). Sensing circuitry 91may include one or more sensors configured to sense a level of currentflow being provided to power source 62 as current I(x,y,z). Sensingcircuitry 91 may also include one or more sensors configured to senseother parameters, such as the temperature of power source 62 and/or atemperature within the device where antenna 63 and power source 62 arelocated. Recharging circuitry 90 may be configured to receive electricalsignals and/or data derived from the electrical signals that are sensedusing sensing circuitry 91, and to control the recharging of powersource 62 based at least in part of these sensed signal and/or theinformation derived from these sensed signals.

Sensing circuitry 91 may include on or more sensors configured tomeasure a voltage level and/or a level of recharge present at powersource 62. Electrical signals and/or information derived from electricalsignals sensed by sensing circuitry 91 that indicate of the voltagelevel and/or a level of recharging that has been competed relative topower source 62 may also be utilized by recharging circuitry 90 as abasis for controlling the recharging of power source 6. For example,recharging circuitry may utilize these signals and/or informationderived from these signals as a basis by to regulate the current beingprovided to power source 62 from node 67 by controlling the couplingprovided between node 67 and power source 62 through switching device92.

In some examples, a shunt device 93, which may comprise an electricallyresistive load, may be coupled to switching device 92 such thatswitching device 92 may couple the shunt device 93 to node 67. Thecoupling of shunt device 93 to node 67 may be utilized to dissipate thecurrent, and thus the energy being imposed on coil 52, 55, and 58, atvarious times when recharging circuitry 90 determines that rechargingcurrent is not to be applied to power source 62 but wherein a rechargingcurrent is being induced into one or more of the coils. In someexamples, recharging circuitry 90 may disconnect the coupling betweennode 67 and power source 62 when a determination is made that therecharging of power source 62 should be terminated, either on atemporary or a permanent basis. When not coupling node 67 to powersource 62, recharging circuitry 90 and switching device 92 may beconfigured to optionally couple or not couple shunt device 93 to node67.

FIG. 4 illustrates an exploded view 70 and an assembled view 86 of amulti-axis antenna 89 according to various examples described in thisdisclosure. The multi-axis antenna 89 as shown in FIG. 4 may be themulti-axis antenna of any of IMD 15A, IMD 15B, and sensor circuits 18 asillustrated and described with respect to FIG. 1 , and/or the multi-axisantenna 40 of device 30 as illustrated and described with respect toFIG. 2 . The multi-axis antenna 89 as shown in FIG. 4 may be configuredas antenna 63, and coupled to one or more additional electrical devices,as illustrated and described with respect to FIG. 3 .

Referring again to FIG. 4 , antenna 89 includes a first coil 71, whichmay be referred to as the X-axis coil, a second coil 76, which may bereferred to as the Y-axis coil, and a third coil 80, which may bereferred to as the Z-axis coil. Each of coils 71, 76, and 80 may beconfigured so that each of the windings forming the coils, respectively,may be positioned relative to a ferrite core 85 so that the windingsencircle a portion of the ferrite core 85, and in some examples mayencircle a portion of one or two of the other coils. For example, firstcoil 71 may be formed as winding of an electrical conductor, such as awire formed of an electrically conductive material such as copper. Theelectrical conductor forming first coil 71 may include a first terminal73 coupled to a first end of the winding, and a second terminal 74coupled to a second end of the winding opposite the first end of thewinding. The first terminal 73 and the second terminal 74 are arrangedto allow the winding forming first coil 71 to be coupled to additionalelectrical devices and/or circuitry, such as one or moretuning/smoothing capacitors, a diode, and/or recharging circuitryconfigured to direct and control a current induced into first coil 71 toallow the induced current to be utilized in recharging a rechargeablepower source of an implanted medical device.

As illustrated in FIG. 4 , first coil 71 is formed of a winding thatencircles a portion of the X-axis of the three-axis coordinate system64, and thus may be referred to as the X-axis coil. The winding formingfirst coil 71 includes an interior space 72 comprising an opening in thewinding that extends through the winding forming first coil 71 along theX-axis, and providing the interior shape of first coil 71 incross-section that is perpendicular to the X-axis. The interior space 72of first coil 71 may comprise an interior shape, such as a square cubicshape, that corresponds to a shape of ferrite core 85 at least withrespect to the sides of ferrite core 85 in cross-section relative to theheight “H” dimension and the depth “D” dimension of ferrite core 85. Thedimensions of the interior space 72 of first coil 71 are at least largeenough to allow first coil 71 to be positioned so that first coil 71encircles at least a portion of the ferrite core 85 around a height anddepth dimension of the ferrite core 85. In some examples, the dimensionsof interior space 72 are large enough to allow one or more of thewindings of second coil 76 and/or third coil 80 to be at least partiallypositioned within interior space 72 and having the winding forming firstcoil 71 encircle at least a portion of the second coil 76 and/or thethird coil 80 while also encircling a portion of the ferrite core 85. Inother examples, the dimensions of interior space 72 of first coil 71 aresuch that the interior space is just sufficiently large enough toencircle the exterior dimensions of core 85.

Similarly, second coil 76 may be formed as winding of an electricalconductor, such as a wire formed of an electrically conductive materialsuch as copper. The electrical conductor forming second coil 76 mayinclude a first terminal 78 coupled to a first end of the winding, and asecond terminal 79 coupled to a second end of the winding opposite thefirst end of the winding. The first terminal 78 and the second terminal79 are arranged to allow the winding forming second coil 76 to becoupled to additional electrical devices and/or circuitry, such as oneor more tuning/smoothing capacitors, a diode, and/or rechargingcircuitry configured to direct and control a current induced into secondcoil 76 to allow the induced current to be utilized in recharging arechargeable power source of an implanted device.

As illustrated in FIG. 4 , second coil 76 is formed of a winding thatencircles a portion of the Y-axis of the three-axis coordinate system64, and thus may be referred to as the Y-axis coil. The winding formingsecond coil 76 includes an interior space 77 comprising an opening inthe winding that extends through the winding forming second coil 76along the Y-axis, and providing an interior shape of second coil 76 incross-section that is perpendicular to the Y-axis. The interior space 77formed by second coil 76 may include a shape, such as a square cubicshape, that corresponds to a shape of ferrite core 85 at least withrespect to the sides of ferrite core 85 in cross-section relative to thewidth “W” dimension and the depth “D” dimension of ferrite core 85. Thedimensions of the interior space 77 of second coil 76 are at least largeenough to allow second coil 76 to be positioned so that second coil 76encircles at least a portion of the ferrite core 85 around a width and adepth dimension of the ferrite core 85. In some examples, the dimensionsof interior space 77 is large enough to allow one or more of thewindings of first coil 71 and/or third coil 80 to be at least partiallypositioned within interior space 77 and having the winding formingsecond coil 76 encircle at least a portion of the first coil 71 and/orthe third coil 80 while also encircling a portion of the ferrite core85. In other examples, the dimensions of interior space 77 of secondcoil 76 are such that the interior space is just sufficiently largeenough to encircle the exterior dimensions of core 85.

Third coil 80 of antenna 89 may be formed as winding of an electricalconductor, such as a wire formed of an electrically conductive materialsuch as copper. The electrical conductor forming third coil 80 mayinclude a first terminal 82 coupled to a first end of the winding, and asecond terminal 83 coupled to a second end of the winding opposite thefirst end of the winding. The first terminal 82 and the second terminal83 are arranged to allow the winding forming third coil 80 to be coupledto additional electrical devices and/or circuitry, such as one or moretuning/smoothing capacitors, a diode, and/or recharging circuitryconfigured to direct and control a current induced into third coil 80 toallow the induced current to be utilized in recharging a rechargeablepower source of an implanted device.

As illustrated in FIG. 4 , third coil 80 is formed of a winding thatencircles a portion of the Z-axis of the three-axis coordinate system64, and thus may be referred to as the Z-axis coil. The winding formingthird coil 80 includes interior space 81 comprising an opening in thewinding that extends through the winding forming third coil 80 along theZ-axis, and providing an interior shape of third coil 80 incross-section that is perpendicular to the Z-axis. The interior space 81of third coil 80 may comprise a shape, such as a square shape, thatcorresponds to a shape of ferrite core 85 at least with respect to thesides of ferrite core 85 in cross-section relative to the height “H”dimension and the width “W” dimension of ferrite core 85. The dimensionsof the interior space 81 of third coil 80 are at least large enough toallow third coil 80 to be positioned so that third coil 80 encircles atleast a portion of the ferrite core 85 around a height and a widthdimension of the ferrite core 85. In some examples, the dimensions ofinterior space 81 are large enough to allow one or more of the windingsof first coil 71 and/or second coil 76 to be at least partiallypositioned within interior space 81 and having the winding forming thirdcoil 80 encircle at least a portion of the first coil 71 and/or thesecond coil 80 while also encircling a portion of the ferrite core 85.In other examples, the dimensions of interior space 81 of third coil 80are such that the interior space is just sufficiently large enough toencircle the exterior dimensions of core 85.

Assembled view 86 illustrates an example of multi-axis antenna 89assembled to include first coil 71, second coil 76, and third coil 80,each coil positioned to encircle some portion of ferrite core 85, andwherein portions of at least two of the coils are at least partiallyencircled by one of the coils. As illustrated by assembly view 86, thefirst coil 71 is positioned around the core 85, and having the windingforming first coil 71 in contact with exterior surfaces of core 85forming the height “H” and the depth “D” dimension of the core. Thethird coil 80 is positioned around the core 85 and encircling at least aportion of the winding forming first coil 71. The second coil 76 ispositioned around the core 85 and encircling at least a portion of thewinding forming first coil 71 and at least a portion of winding formingthird coil 80. When assembled as shown in assembly view 86, core 85 maybe included, at least partially within interior space 72 of first coil71, wherein core 85 and first coil 71 may be included, at leastpartially, within interior space 81 of third coil 80, and wherein core85, first coil 71, and third coil 80 may be included, at leastpartially, within interior space 77 of second coil 76.

When assembled as shown in assembly view 86, at least one coil of firstcoil 71, second coil 76, and third coil 80 has an axis of orientationthat corresponds with one of the X-axis, the Y-axis, and the Z-axis,respectively, of the three-axis coordinate system 64. As such, any angleof orientation of a magnetic field that may be imposed upon theassembled antenna 89 may induce a current in at least one of the coilsforming antenna 89, and for example when coupled as a receive antenna inan implantable medical device. As such, any orientation of themulti-axis antenna 89 being configured to have currents induced in thecoils of the antenna relative to an externally generated magnetic fieldor magnetic fields imposed on the antenna may generate a current in atleast one of coils 71, 76, and/or 80 regardless of the orientation ofthe direction of the magnetic field relative to the orientation of theantenna 89. These induced current or currents may be applied to arechargeable power source coupled to the antenna 89 for the purpose ofrecharging the power source. As described, these induced currents may beprovided by antenna 89 irrelevant of the orientation of the direction ofthe magnetic field or magnetic fields impose on the antenna 89 becauseof the orthogonal arrangement of the orientations of the three coils ofthe antenna 89 relative to each other.

The order in which the assembly of the coils 71, 76, and 80 is providedrelative to the core 85, e.g., the layering of the coils relative to oneanother, is not limited to any particular arrangement or to anyparticular order. For example, any one of coils 71, 76, or 80 may bepositioned in assembly view 86 as closest to core 85, with the remainingcoils positioned in any order so that the coil positioned closest tocore 85 in included, at least partially within the interior space of theremaining two coils. The coil of coils 71, 76, and 80 that is positionedas the outermost layer of assembly view 86 may be configured so that aleast a part of core 85 and the two additional coils are positioned, atleast partially, within the interior space of the outer most coil.

As shown in the assembly view 86, a first set of terminals terminal ofeach of first coil 71, second coil 76, and third coil 80 (e.g., firstterminals 73, 78, and 82) may extend from a common point, e.g., from aposition proximate to a same corner of core 85, illustrated in FIG. 4 asleads 87. In addition, a second set of terminals of each of first coil71, second coil 76, and third coil 80 (e.g., second terminals 74, 79,and 83) may extend from a common point, e.g., from a position proximatea same corner of core 85 illustrated in FIG. 4 as leads 88. Leads 87 mayextend from a same corner of assembly view 86 as a corner proximate toleads 88, or leads 87 may extend from a first corner of assembly view86, and leads 88 may extend from a second and different corner ofassembly view 86. Having leads 87 and 88 extend from a same corner, orhaving lead 87 extend together from a first corner and having lead 88extend from a second different corner, may allow connection of theseleads to additional electronic devices and/or electrical circuitry to bemade using less space and/or less additional conductive leads within theimplantable medical device, and thus further the advantages obtained byuse of the multi-axis antenna 89. For example, one set of leads 87 or 88may all be coupled to a common point, such as common voltage node 68illustrated in schematic diagram 50 in FIG. 3 . As illustrated in FIG. 4, having at least one set of leads 87 or 88 exit assembly view 86 of theantenna at a common point may therefore reduce the number of individualconductors that may need to extend within the device where antenna 89 islocated, and thus help further minimum the amount of space, and thus insome examples the overall size of the device.

As illustrated in FIG. 4 , the height “H” dimension, the width “W”dimension, and the depth “D” dimension of ferrite core 85 may be equalin value so that core 85 forms a cubic volume. In some examples, thevalue for each of the height, width, and depth dimensions of core 85 areeach three millimeters (mm), providing an overall volume for core 85 oftwenty-seven cubic millimeters (mm³). However, the value for thedimension for any give one of the height, width, and depth dimension arenot limited to having a same value, and may have different values thatrender the overall shape of ferrite core 85 to some shape other than acube. For example, the ferrite core 85 may provide a spherical shapedouter surface over which the coil or coils forming the multi-axisantenna are positioned. In other examples, ferrite core 85 may beprovided in the shape of an upright cylinder, having a square, circular,or elliptical shape in cross-section. Further, the material used to formcore 85 is not limited to a particular type of material, and in someexamples, is a ferrite material comprising a compound that includes ironoxides, and may be combined with nickel, zinc, and or manganesecompounds. The ferrite material used to form core 85 may include “softferrites” that have low coercivity (magnetization in the material can beeasily revered in direction without generated large levels of hysteresislosses) and having high resistivity, which helps reduce eddy currentflowing in the material.

The electrical conductor used to form the windings of first coil 71,second coil 76, and third coil 80 are not limited to being formed fromany particular type of material, and may be formed from a conductivemetal, such as copper, that is easily formed into a wire and may beeasily bent to form the desired shape of the winding for each of thecoils. The electrical conductors in some examples may include aninsulative material, such as enamel, coated over the exterior surface ofthe conductor to provide an insulative layer between the individualwindings of a single one of the coils, and also between winding ofdifferent coils that may be brought into contact with one another aspart of the assembly used to form antenna 89. In various examples, theelectrical conductor used to form the windings of each coil is Litzwire, for example a single or multiple stranded wire, wherein theelectrical conductor used to form each winding is insulated along theouter surface of the electrical conductor, for example using a coating,such as enamel, to reduce the skin effect of the electrical conductor.Skin effect is the characteristic of electrical current flowing throughan electrical conductor that causes the flow of current in theelectrical conductor to travel though the outer portion, e.g., the“skin” of the conductor, and not through the inner portion of theelectrical conductor. The skin effect is more pronounced at higherfrequencies. The use of Litz wire helps reduce the skin effect in theelectrical conductor at higher frequencies.

In addition, the inter-turn capacitance of the respective windings/turnsis reduced by increasing inter-turn distances, thus increasing theself-resonant frequency of the assembly and enabling higher modulationfrequency to be applied to the coil. In addition, the overall shape of acoil formed to encircle a portion of ferrite core 85 may not encircle aninterior space within the coil itself that conforms to the shape of theportion of the ferrite core 85 encircled by the coil. For example, thewindings of the coil may extend outward away from certain portions ofthe surface of the ferrite core 85 while contacting other portions ofthe ferrite core, so the that the shape of the interior portion of thecoil does not correspond exactly to the shape of the exterior portion ofthe ferrite core 85 that the coil encircles. In one example, the ferritecore may be cubic in shape, while the windings forming the coilsencircling the ferrite core may be shaped more like a rounded-cornersquare with sides of the square shape that are arc-shaped rather thanbeing linear, the arc-shaded sided extending outward from a center pointof the interior space encircled by the coil winding between the cornersof the rounded-corner square.

In one specific example, each of the first coil 71, second coil 76, andthird coil 80 comprise a winding respectively formed with 10/46 Litzwire, using 10 turns of wire per coil and the winding formed on a 3 mmby 3 mm by 3 mm ferrite cube. Using an antenna having coils wound inthis manner, a 20 milliampere-hour (mAh) rechargeable battery implantedat a depth of approximately 15 centimeters within a body of a patientmay be recharged in approximately sixty minutes. In some examples, the20 mAh battery may be expected to be able to provide power to animplanted medical device, such as device 30 as illustrated and describewith respect to FIG. 2 for a period of at least one year. As such, theneed to perform a recharging process on a power source of an implantedmedical device may be minimized, for example to a period ofapproximately one hour, and thus reduce the cost, inconvenience and theneed for repeated visits for example to a clinic or hospital in order tomaintain a proper power for an implanted medical device. Further thetime to recharge the implanted medical device using the multi-axisantenna may be relatively fast. For example, using the multi-axisantenna described in this paragraph, an 18 mAh battery may be chargedfrom 0.38 volts to a voltage level of 2.6 volts in approximately 30minutes with any random orientation between the magnetic field imposedon the implanted device at a depth of 15 centimeters for implantationwhile maintaining acceptable levels of electromagnetic exposure for thepatient. Examples of batteries that may be charged using the multi-axisantenna described in this paragraph are not limited to these mAh orvoltage ratings, and for example may include batteries having larger orsmaller mAh ratings, and other voltage ranges, such as 0.0 to 4.5 volts.

Examples of antenna 89 are described as comprising a ferrite core 85.However, examples of antenna 89 may also comprise coils 71, 76, and 80having orthogonal axis of orientation and assembled as illustrated anddescribed above as shown in assembly view 86, but without the ferritecore 85. In some examples, the assembly of coils 71, 76, and 80 may beformed on a core formed of a non-ferrite material, such as anon-conductive plastic. In some examples, the assembly of coils 71, 76,and 80 may be formed without use of a core of any type, and thus havingthe interior space of assembly formed as an opening or hollow space.

Further, the use of the multi-axis antenna that is not orientationspecific with respect to the orientation of the receive antenna withinthe implanted medical device and the direction of the magnetic fieldbeing imposed on the implanted device to recharge the device mayeliminate the need for, and thus reduce the cost associated with,equipment and methods required to align the magnetic fields with aparticular orientation of an antenna. In some examples, a singlerecharging coil, such as a spiral wound planar coil, or a single pair ofrecharging coils (for example arranged as a Helmholtz coil), may be allthat is required for use as the recharging coil or coils providing themagnetic field used to induce currents into the receive antenna of theimplanted medical device while providing at least a minimum level ofinduced currents for a given magnetic field strength regardless of therelative orientation of the imposed magnetic field relative to theorientation of the implanted device.

FIG. 5 illustrates a set of graphical diagrams 100, 104, 108, and 110,of imposed magnetic field intensities versus induced power as providedby individual coils and a combination of coils of a multi-axis antennaaccording to various examples described in this disclosure. Graphicaldiagram 100 is illustrative of an example of resulting power levelsdelivered to a load, (e.g., a battery of an implanted medical device),as represented by curve 101, for different magnetic field intensitiesgenerated by a sinusoidal current applied to a transmit coil and imposedat a predefined distance from the transmit coil onto a first coil of amulti-axis antenna of an implantable medical device. Graphical diagram100 includes an X-axis representing levels of magnetic field intensity“H” measured in amperes per meter (A/m) at the first coil of themulti-axis antenna. The vertical axis of graphical diagram 100represents of the resultant power delivered to the load (PDL), inmilliwatts (mW), the load representative in some example of the batteryof the implanted medical device that is being recharged. Curve 101represents measured resultant power induced into an example of an X-axiscoil of a multi-axis antenna as described for example with respect toFIG. 4 . Referring again to FIG. 5 , when measuring the resultant power,the first coil was located at a distance of 15 centimeters from thetransmit coil generating the magnetic fields, the distancerepresentative of a possible location within a patient for a deeplyimplanted medical device. For the measurements of the induced powerlevels illustrated as curve 101, the direction of the magnetic fieldimposed on the first coil (the X-axis coil) of the multi-axis antennacorresponds to the direction, e.g., was colinear with, the orientationof the X-axis coil. Having the direction of the magnetic fieldcorresponding with the direction of orientation of the X-axis coil,(e.g., magnetic field direction was the same orientation as the normalaxis of orientation of the X-axis coil), should provide a maximum levelof coupling efficiency between the magnetic field and the X-axis coil,and thus generate the highest level of power induced into the X-axiscoil for the given level of magnetic field intensity imposed onto themulti-axis antenna.

Graphical diagram 104 is illustrative of an example of resulting powerlevels delivered to a load, (e.g., a battery of an implanted medicaldevice), as represented by curve 105, for different magnetic fieldintensities generated by a sinusoidal current applied to a transmit coiland imposed at a predefined distance from the transmit coil onto asecond coil of the receive antenna of same implantable medical deviceused to generate the data illustrated in graphical diagram 100.Graphical diagram 104 includes an X-axis representing levels of magneticfield intensity “H” measured in amperes per meter (A/m) at the secondcoil of the multi-axis antenna. The vertical axis of graphical diagram104 represents of the resultant power delivered to the load (PDL), inmilliwatts (mW), the load representative in some examples of the batteryof the implanted medical device that is being recharged. Curve 105represents measured resultant power induced into an example of a Y-axiscoil of a multi-axis antenna as described with respect to FIG. 4 .Referring again to FIG. 5 , when measuring the resultant power, thesecond coil was located at the same 15 centimeters distance from thetransmit coil generating the magnetic fields as was used when measuringthe power delivered to the load in graphical diagram 100. For themeasurements of the induced power levels illustrated by curve 105 ofgraphical diagram 104, the direction of the magnetic field imposed onthe second coil (the Y-axis coil) of the multi-axis antenna correspondsto the direction, e.g., was colinear with, the orientation of the Y-axiscoil. Having the direction of the magnetic field corresponding with thedirection of orientation of the Y-axis coil, (e.g., magnetic fielddirection was the same orientation as the normal axis of orientation ofthe Y-axis coil), should provide a maximum level of coupling efficiencybetween the magnetic field and the Y-axis coil, and thus generate thehighest level of power induced into the Y-axis coil for the given levelof magnetic field intensity imposed onto the multi-axis antenna.

Graphical diagram 108 is illustrative of an example of resulting powerlevels delivered to a load, (e.g., a battery of an implanted medicaldevice), as represented by curve 109, for different magnetic fieldintensities generated by a sinusoidal current applied to a transmit coiland imposed at a predefined distance from the transmit coil onto a thirdcoil of the receive antenna of same implantable medical device used togenerate the data illustrated in graphical diagrams 100 and 104.Graphical diagram 108 includes an X-axis representing levels of magneticfield intensity “H” measured in amperes per meter (A/m) at the thirdcoil of the multi-axis antenna. The vertical axis of graphical diagram108 represents of the resultant power delivered to the load (PDL), inmilliwatts (mW), the load representative in some examples of the batteryof the implanted medical device that is being recharged. Curve 109represents measured resultant power induced into an example of a Z-axiscoil of a multi-axis antenna as described with respect to FIG. 4 .Referring again to FIG. 5 , when measuring the resultant power, thethird coil was located at the same 15 centimeters distance from thetransmit coil generating the magnetic fields as was used when measuringthe power delivered to the load in graphical diagrams 100 and 104. Forthe measurements of the induced power levels illustrated by curve 109 ofgraphical diagram 108, the direction of the magnetic field imposed onthe third coil (the Z-axis coil) of the multi-axis antenna correspondsto the direction, e.g., was colinear with, the orientation of the Z-axiscoil. Having the direction of the magnetic field corresponding with thedirection of orientation of the Z-axis coil, (e.g., magnetic fielddirection was the same orientation as the normal axis of orientation ofthe Z-axis coil), should provide a maximum level of coupling efficiencybetween the magnetic field and the Z-axis coil, and thus generate thehighest level of power induced into the Z-axis coil for the given levelof magnetic field intensity imposed onto the multi-axis antenna.

For each of graphical diagrams 100, 104, and 108, a resultant powerlevel applied to the load remains at zero mW or nearly zero mW of powerfor any applied level of magnetic field intensities up to approximately40 A/m. This is due to the fact that a minimum level of magnetic fieldintensity must be applied to any given one of the first, second, orthird coils of the multi-axis antenna in order to generate a voltagelevel at the coil that is adequate to overcome the forward biasingvoltage level for the individual diode coupled in series with thatparticular coil. Once a voltage that is adequate to overcome the biasingvoltage of the diode associated with a given coil has been generatedwithin that coil of the multi-axis antenna, that coil will begin toprovide a current flow, and thus begin to deliver power to the load.

For example, when a magnetic field intensity in excess of 40 A/m isapplied to the first coil, the level of power delivered to the load bythe first coil begins to increase from a non-zero value in somerelationship based on the level of the applied magnetic field intensity,as indicated by curve 101. As shown by curve 101, the power delivered tothe load by the first coil exceeds 40 mW when a magnetic field intensityof 120 A/m is imposed on the first coil, as illustrated by graphicaldiagram 100. When a magnetic field intensity in excess of 40 A/m isapplied to the second coil, the level of power delivered to the load bythe second coil begins to increase from a non-zero value in somerelationship based on the level of the applied magnetic field intensity,as indicated by curve 105. As shown by curve 105, the power delivered tothe load by the second coil exceeds 40 mW when a magnetic fieldintensity of 120 A/m is imposed on the second coil, as illustrated bygraphical diagram 104. When a magnetic field intensity in excess of 40A/m is applied to the third coil, the level of power delivered to theload by the third coil begins to increase from a non-zero value in somerelationship based on the level of the applied magnetic field intensity,as indicated by curve 109. As shown by curve 109, the power delivered tothe load by the third coil exceeds 40 mW when a magnetic field intensityof 120 A/m is imposed on the third coil, as illustrated by graphicaldiagram 108.

Each of graphical diagrams 100, 104, and 108 illustrate curvesrepresentative of measured resultant power levels induced into thefirst, second, and third coils, respectively, of a multi-axis antennawherein for each diagram, the magnetic field imposed on each coil,respectively, was oriented to have a direction that corresponds to theaxis of orientation (normal axis) for the coil being measured forinduced power levels. Graphical diagram 110 is illustrative of anexample of resultant power levels delivered to a load, (e.g., a batteryof an implanted medical device), as represented by curve 111, fordifferent magnetic field intensities generated by a sinusoidal currentapplied to a transmit coil and imposed at the predefined distance fromthe transmit coil onto each of the three coils of a multi-axis antennaof the same implantable medical device used to generate the dataillustrated in graphical diagrams 100, 104, and 108. When imposing themagnetic fields onto the multi-axis antenna to measure power levelsdelivered by all three of the coils of the multi-axis antenna combined,the direction of the magnetic field was random, and did not necessarilyalign with any axis of orientation (e.g., a normal axis of orientation)for any of the first, second, or third coils of the multi-axis antenna.

Graphical diagram 110 includes an X-axis representing levels of magneticfield intensity “H” measured in amperes per meter (A/m) at themulti-axis antenna. The vertical axis of graphical diagram 110represents of the resultant power delivered to the load (PDL), inmilliwatts (mW), the load representative in some examples of the batteryof the implanted medical device that is being recharged. Curve 1111represents measured resultant power induced into an example of themulti-axis antenna as described with respect to FIG. 4 . Referring againto FIG. 5 , when measuring the resultant power, the multi-axis antennawas located at the same 15 centimeters distance from the transmit coilgenerating the magnetic fields as was used when measuring the powerdelivered to the load in graphical diagrams 100, 104, and 108. Thelevels of power delivered to the load as illustrated by curve 111 ingraphical diagram 110 indicate a combined level of power delivered bythe three coils of the multi-axis antenna, but wherein the direction ofthe magnetic field imposed onto the multi-axis antenna had a randomorientation relative to the orientation of the three coils and themulti-axis antenna.

As illustrated by graphical diagram 110, a level of power delivered tothe load by the multi-axis antenna includes power levels at any givenlevel of imposed magnetic field intensity that are similar in magnitudeto the levels of power provided by any one of the individual coils asindicated in graphical diagrams 100, 104, and 108 for a same level ofmagnetic field intensity. However, a random orientation of the magneticfield direction of the imposed magnetic fields was applied to themulti-axis antenna when measuring the PDL level indicated by curve 111.When applying the magnetic fields having the random orientation for themagnetic field direction to all three of the coils of the multi-axisantenna, the resultant power level applied to the load remained at azero mW, or at nearly zero mW levels of power for any applied magneticfield intensities up to approximately 40 A/m. When the level of theimposed magnetic field intensity exceeded 40 A/m, and still having therandom direction of orientation relative to the multi-axis antenna, thelevel of power delivered to the load by the multi-axis antenna begins toincrease from the non-zero value in some relationship based on the levelof the applied magnetic field intensity, as indicated by curve 111. Asshown by curve 111, the power delivered to the load by the multi-axisantenna follows a curve 111 corresponding to the curves 101, 105 and 109of the individual coils of the antenna, and for example providesapproximately 40 mW of power to the load when a magnetic field intensityof 120 A/m is imposed on the multi-axis antenna, as illustrated ingraphical diagram 110.

The measured values for PDL as illustrated by graphical diagrams 110,104, 108, and 110 demonstrate that the multi-axis antenna may deliver asimilar level of power to a load for a given level of magnetic fieldintensity imposed on the coils of the multi-axis antenna, but with arandom orientation of the antenna relative to a direction of the imposedmagnetic field compared to a “best scenario” alignment of the directionof the imposed magnetic field relative to a given coil of the antenna.As such, the performance of the multi-axis antenna can be the same orcomparable to a planar or single-axis antenna when a magnetic fieldfully aligned with the axis of the planar or signal axis antenna is usedto induce power into the planar or single-axis antenna, but without theneed for alignment of the direction of the magnetic field being imposedonto the multi-axis antenna with an axis of orientation of any of thecoils forming the multi-axis antenna. This feature of not requiring analignment in order to induce a level of power into the multi-axisantenna may provide the benefit of allowing a minimum level of inductivecoupling to be obtained between a transmit coil and the multi-axisantenna of an implanted device without the need for an elaboratealignment procedure to be performed, and/or without the need foradditional equipment needed to position and align the transmit coil. Theadvantages of the lack of need for alignment of the transmit coil may beparticularly beneficial for recharging devices that may be implantedwithin a location a ventricle of a heart of a patient, such as device 30as illustrated and described with respect to FIG. 2 . These types ofimplants may allow the device to move to some degree after beingimplanted, for example in response to heartbeats of the patient. Assuch, maintaining continuous alignment of the direction of a magneticfield generated by a transmit coil to an axis of orientation of a planaror single axis antenna of an implanted device may be difficult orimpossible due to the continued movement of the device. The ability toachieve a same and minimum level of inductive coupling between atransmit coil providing a magnetic field being imposed onto themulti-axis antenna of a device that may be moving may provide anadditional benefit of efficient recharging of these type devicescompared to similar device that may comprise a planar or single axisreceive antenna within or coupled to the device to be recharged.

FIG. 6 is a functional block diagram illustrating an exampleconfiguration of an IMD 15 according to various examples described inthis disclosure. IMD 15 may correspond to any of IMD 15A and IMD 15Bdescribed and illustrated with respect to FIG. 1 and/or device 30 asdescribed and illustrated with respect to FIG. 2 , or another IMDconfigured to be rechargeable using the devices, systems, and methods asdescribed in this disclosure. IMD 15 includes a power source 124 thatmay be coupled to the electronic circuitry provided in IMD 15, and isconfigured to provide electrical power to these circuits. IMD 15 may beinductively rechargeable by imposing one or more magnetic fields ontoIMD 15, wherein energy from these imposed field(s) may induce anelectrical energy into antenna 129 coupled to communication circuitry125 and to device recharging circuitry 126, or into an antenna 131 thatmay be provided in addition to antenna 129 and that when provided, isalso coupled to recharging circuitry 126. When configured to be used forrecharging IMD 15, antenna 129 and/or antenna 131 may be a multi-axisantenna according to any of the examples of multi-axis antennasdescribed in this disclosure, or any equivalents thereof. IMD 15 may bean example of a deeply implanted device, such as a device implantedwithin a chamber of the heart of a patient, and including a multi-axisantenna as described in this disclosure that allows efficient rechargingof a power source (e.g., power source 124) located within the IMD usinga random orientation of a magnetic field imposed on the IMD to rechargethe power source.

As shown in FIG. 6 , device recharging circuitry 126 is coupled to powersource 124, and may be coupled through switching device 130 to receiveelectrical energy induced in antenna 129 (or in antenna 131 whenprovided) by one or more electromagnetic fields imposed on the antenna,and to regulate the energy to provide a level of energy that is providedto power source 124 for the purpose of recharging power source 124and/or powering the other circuitry included as part of IMD 15. Devicerecharging circuitry 126 may perform various energy conditioningfunctions to the energy inductively generated in antenna 129 (or antenna131 when provided), for example by providing rectification, voltagelevel regulation, current level regulation, and/or other signalprocessing functions in order to generate the “recharging energy”provided to power source 124. Antenna 129 (and/or antenna 131 whenprovided) may be a multi-axis antenna that is not orientation specificwith respect to the coupling efficiency of the inductive charging ofpower source 124 based on the orientation of the antenna relative to theorientation of the coil or coils providing the magnetic field(s)intended to recharge power source 124.

Thus, IMD 15 may be configured to couple magnetic energy captured by anantenna (including, but not necessarily a telemetry antenna), directedinto a suitable rectifying circuit that delivers the electrical energyto an energy storage device such as a rechargeable battery. Theswitching device 130, which may be a transistor, may be included in IMD15 and may be controlled, for example by processing circuitry 120, toselect whether the telemetry or the power recharge system is active, andthus whether multi-axis antenna 129 is coupled to the communicationcircuitry 125 or the device recharging circuitry 126. In other examples,the second antenna 131 is coupled directly to device rechargingcircuitry 126, and is configured to receive the inductively coupledenergy provided to antenna 131, and to provide the inductively coupledenergy to device recharging circuit 126 to recharge power source 124.

In the illustrated example, IMD 15 includes processing circuitry 120 andan associated memory 121, sensing circuitry 122, therapy deliverycircuitry 123, one or more sensors 127, and the communication circuitry125 coupled to antenna 129 as describe above. However, IMD 15 need notinclude all of these components, or may include additional components.For example, IMD 15 may not include therapy delivery circuitry 123 insome examples of the device. Memory 121 includes computer-readableinstructions that, when executed by processing circuitry 120, causes IMD15 and processing circuitry 120 to perform various functions attributedto IMD 15 and processing circuitry 120 as described herein (e.g.,preparing information for transmission from IMD 15 regarding a level ofcharge present in a power source, such as a battery management systeminformation (BMS)). For example, processing circuitry 120 may beconfigured to provide information including a state of charge, and/ortemperature information related to a battery, e.g., a battery located inIMD 15, determining a level of inductive coupling, e.g., energy levelbeing generated in an antenna located in IMD 15 as a result of anelectromagnetic field or fields being imposed on IMD 15, and generateinformation related to this inductively received energy for transmissionby the communication antenna or separate antenna and associated powerconditioning circuitry of IMD 15.

Memory 121 may include any volatile, non-volatile, magnetic, optical, orelectrical media, such as a random-access memory (RAM), read-only memory(ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM(EEPROM), flash memory, or any other digital or analog media. Memory 121may store threshold(s) for time of day, posture, heart rate, activitylevel, respiration rate, and other parameters. Memory 121 may also storedata indicating cardiovascular pressure measurements, and store otherdata associated with cardiac and/or other physiological eventsassociated with a patient.

Processing circuitry 120 may include fixed function circuitry and/orprogrammable processing circuitry. Processing circuitry 120 may includeany one or more of a microprocessor, a controller, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield-programmable gate array (FPGA), or equivalent discrete or analoglogic circuitry. In some examples, processing circuitry 120 may includemultiple components, such as any combination of one or moremicroprocessors, one or more controllers, one or more DSPs, one or moreASICs, or one or more FPGAs, as well as other discrete or integratedlogic circuitry. The functions attributed to processing circuitry 120herein may be embodied as software, firmware, hardware or anycombination thereof.

As illustrated, sensing circuitry 122 and therapy delivery circuitry 123are coupled to electrodes 132. Electrodes 132 as illustrated in FIG. 6may correspond to, for example, electrodes located on leads 21 and 22and/or the housing 23 of IMD 15A (FIG. 1 ), or electrodes 32 and 33 ofdevice 30 (FIG. 2 ). Sensing circuitry 122 in IMD 15 as shown in FIG. 6may monitor signals from a selected two or more of electrodes 132 inorder to monitor electrical activity of heart, impedance, or some otherelectrical phenomenon. Sensing of a cardiac electrical signal may bedone to determine heart rates or heart rate variability, or to detectarrhythmias (e.g., tachyarrhythmias or bradycardia) or other electricalsignals. In some examples, sensing circuitry 122 may include one or morefilters and amplifiers for filtering and amplifying a signal receivedfrom electrodes 132.

In some examples, sensing circuitry 122 may sense or detectphysiological parameters, such as heart rate, blood pressure,respiration, and other physiological parameters associated with apatient. The resulting electrical signals may be passed to cardiac eventdetection circuitry that detects a cardiac event for example when acardiac electrical signal crosses a sensing threshold. The cardiac eventdetection circuitry may include a rectifier, filter and/or amplifier, asense amplifier, comparator, and/or analog-to-digital converter. Sensingcircuitry 122 may output an indication to processing circuitry 120 inresponse to sensing of a cardiac event (e.g., detected P-waves orR-waves).

In this manner, processing circuitry 120 may receive detected cardiacevent signals corresponding to the occurrence of detected R-waves andP-waves in the respective chambers of heart. Indications of detectedR-waves and P-waves may be used for detecting ventricular and/or atrialtachyarrhythmia episodes, e.g., ventricular or atrial fibrillationepisodes. Some detection channels may be configured to detect cardiacevents, such as P-waves or R-waves, and provide indications of theoccurrences of such events to processing circuitry 120, e.g., asdescribed in U.S. Pat. No. 5,117,824 to Keimel et al., which issued onJun. 2, 1992 and is entitled, “APPARATUS FOR MONITORING ELECTRICALPHYSIOLOGIC SIGNALS,” and is incorporated herein by reference in itsentirety.

Sensing circuitry 122 may also include switching circuitry to selectwhich of the available electrodes 132 (or electrode polarities) are usedto sense the heart activity. In examples with several electrodes 132,processing circuitry 120 may select the electrodes that function assense electrodes, i.e., select the sensing configuration, via theswitching circuitry within sensing circuitry 122. Sensing circuitry 122may also pass one or more digitized EGM signals to processing circuitry120 for analysis, e.g., for use in cardiac rhythm discrimination.

In the example of FIG. 6 , IMD 15 includes one or more sensors 127coupled to sensing circuitry 122. Although illustrated in FIG. 6 asincluded within IMD 15, one or more of sensors 127 may be external toIMD 15, e.g., coupled to IMD 15 via one or more leads, or configured towirelessly communicate with IMD 15. In some examples, sensors 127transduce a signal indicative of a patient parameter, which may beamplified, filtered, or otherwise processed by sensing circuitry 122. Insuch examples, processing circuitry 120 determines values of patientparameters based on the signals. In some examples, sensors 127 determinethe patient parameter values, and communicate them, e.g., via a wired orwireless connection, to processing circuitry 120.

In some examples, sensors 127 include one or more accelerometers 128,e.g., one or more three-axis accelerometers. Signals generated by theone or more accelerometers 128 may be indicative of, as examples, grossbody movement (e.g., activity) of the patient, patient posture, heartsounds or other vibrations or movement associated with the beating ofthe heart, or coughing, rales, or other respiration abnormalities.Accelerometers 128 may produce and transmit signals to processingcircuitry 120 for a determination as to the posture of the patient. Invarious examples, signals from the accelerometers 128 are processed todetermine an activity, such as when the patient is taking a step orsteps, or for example when the patient is running, and used to providean activity count associated with patient initiated physical activity ofthe patient. In some examples, sensors 127 may include sensorsconfigured to transduce signals indicative of blood flow, oxygensaturation of blood, or patient temperature, and processing circuitry120 may determine patient parameters values based on these signals. Invarious examples, sensors 127 may include one or a combination of sensorcircuits 18 (FIG. 1 ) as previously described.

In some examples, processing circuitry 120 determines one or morepatient parameter values based on pressure signals. Patient parametervalues determined based on pressure may include, as examples, systolicor diastolic pressure values, such as pulmonary artery diastolicpressure values. In some examples, a separate device such as sensorcircuits 18 (FIG. 1 ), include one or more sensors and sensing circuitryconfigured to generate a pressure signal, and processing circuitry 120determines patient parameter values related to blood pressure based oninformation received from IMD 15.

Therapy delivery circuitry 123, when provided as part of IMD 15, may beconfigured to generate and deliver electrical therapy to the heart.Therapy delivery circuitry 123 may include one or more pulse generators,capacitors, and/or other components capable of generating and/or storingenergy to deliver as pacing therapy, defibrillation therapy,cardioversion therapy, other therapy or a combination of therapies. Insome instances, therapy delivery circuitry 123 may include a first setof components configured to provide pacing therapy and a second set ofcomponents configured to provide anti-tachyarrhythmia shock therapy. Inother instances, therapy delivery circuitry 123 may utilize the same setof components to provide both pacing and anti-tachyarrhythmia shocktherapy. In still other instances, therapy delivery circuitry 123 mayshare some of the pacing and shock therapy components while using othercomponents solely for pacing or shock delivery.

Therapy delivery circuitry 123 may include charging circuitry, one ormore charge storage devices, such as one or more capacitors, andswitching circuitry that controls when the capacitor(s) are dischargedto electrodes 132 and the widths of pulses. Charging of capacitors to aprogrammed pulse amplitude and discharging of the capacitors for aprogrammed pulse width may be performed by therapy delivery circuitry123 according to control signals received from processing circuitry 120,which are provided by processing circuitry 120 according to parametersstored in memory 121. Processing circuitry 120 controls therapy deliverycircuitry 123 to deliver the generated therapy to the heart via one ormore combinations of electrodes 132, e.g., according to parametersstored in memory 121. Therapy delivery circuitry 123 may include switchcircuitry to select which of the available electrodes 132 are used todeliver the therapy, e.g., as controlled by processing circuitry 120.

Communication circuitry 125 includes any suitable hardware, firmware,software or any combination thereof for communicating with anotherdevice, such as an external device 11, transceiver 16, or another IMD orsensors, such as sensor circuits 18, as shown in FIG. 1 and FIG. 2 .Referring again to FIG. 6 , under the control of processing circuitry120, communication circuitry 125 may receive downlink telemetry from andsend uplink telemetry to external device 11 or another device with theaid of an antenna, such as antenna 129, which may be internal and/orexternal. In some examples, communication circuitry 125 may communicatewith a local external device, for example through transceiver 16, andprocessing circuitry 120 may communicate with a networked computingdevice via the local external device and a computer network, such as theMedtronic® CareLink® Network developed by Medtronic, plc, of Dublin,Ireland.

As described above, in some examples (i.e., where a single antenna isused) the antenna signal can be switched from the telemetrycommunication circuitry 125 to the recharging circuitry 126. In otherexamples the recharge antenna/coil is separate from thecommunication/telemetry antenna. For example, antenna 129 may beswitched between being coupled to communication circuitry 125 and devicerecharging circuitry 126 by switching device 130, wherein switchingdevice 130 may be controlled by processing circuitry 120 to determinewhen antenna 129 is coupled to the communication circuitry 125 and whenantenna 129 is to be coupled to the device recharging circuitry 126.

In various examples, processing circuitry 120 is coupled to devicerecharging circuitry 126, and receives information, such as a level ofcurrent, that is being induced in antenna 129 or antenna 131 as a resultof electrical energy received by the antenna via magnetic energy imposedon IMD 15 for the purpose of recharging power source 124. Processingcircuitry 120 may provide this and other information, for example chargerate and temperature information associated with the power source 124,in the form of an output signal to communication circuitry 125 fortransmission from IMD 15 to one or more external devices, such astransceiver 16. This transmitted information may be used by the externaldevice(s) to control one or more aspects of the recharging process. Forexample, positioning and/or a level of power being applied to arecharging coil or a pair of coils located externally to IMD 15 andgenerating the magnetic field or fields being imposed on IMD 15 may becontrolled using this information transmitted from IMD 15. The settingof electrical parameters used to energize the coil of the pair of coilsgenerating the magnetic field or fields imposed onto IMD 15 for thepurpose of recharging the power source 124 may be controlled using thisinformation transmitted from IMD 15. In addition, other information suchas temperature and field intensity information transmitted from IMD 15,may be used to control the recharging process, for example by regulatingthe field strength being generated by the external coil(s), or forexample to shut off the external coil(s) to stop the recharging process.

A clinician or other user may retrieve data from IMD 15 using externaldevice 11 or another local or networked computing device configured tocommunicate with processing circuitry 120 via communication circuitry125, for example through a transceiver such as transceiver 16. Theclinician may also program parameters of IMD 15 using external device 11or another local or networked computing devices. In some examples, theclinician may select patient parameters used to determine times of dayand target activity levels to determine when to trigger takingmeasurements using sensors 127, accelerometers 128, and or via sensingcircuitry 122.

In various examples, processing circuitry 120 is configured to receivesignals from sensing circuitry 122, sensors 127 including accelerometers128, and/or sensor signals provided by sensors external to IMD 15, toprocess these sensor signals to generate one or more input parametersbased either directly on or derived from the sensor signals. The inputparameters are associated with the value(s) for one or morephysiological parameters associated with a patient, such as patient 12where the IMD 15 may be implanted. The physiological parametersassociated with the input parameters may include activity counts,respiration rates, breathing rates, movements, postures, and changes inpostures associated with a patient. The values associated with theseinput parameters can be values measured directly from the inputparameters, or derived for these input parameters. For example, a valueof a heartrate, measured for example in heartbeats per minute or cardiaccycle length, may be determined as the current value (e.g., the mostrecent value) for the input parameter associated with the heart rate ofthe patient measured over some predefined time period. Similarly, avalue of a breathing rate, measured for example in breaths per minute orbreathing cycle length, may be determined as the current value (e.g.,the most recent value) for the input parameter associated with thebreathing rate of the patient as measured over some predefined timeperiod.

Similarly, the values can be determined for other input parameters, suchas activity count (e.g., based on movement of the patient measured forexample in steps taken by the patient per minute), body temperature, andfor example a current value for a posture of the patient (e.g., lyingdown, standing, sitting). A current value of a physiological parametermay be, in some examples, a mean or median of measured values over aperiod of time. These parameters may be used to monitor the physicalcondition of a patient, and/or to determine the efficacy of a therapybeing applied to the patient, and/or the need to apply a new ordifferent therapy, such as a new or different electrical stimulationtherapy, to the patient based on analysis if the sensed parametersand/or instructions received by IMD 15 from one or more externaldevices.

FIG. 7 is a functional block diagram illustrating an exampleconfiguration of a system 140 for inductive recharging of an implantablemedical device 15 according to various examples described in thisdisclosure. System 140 includes recharging circuitry 141 electricallycoupled to a single recharging coil 142 in some examples, or a pair ofrecharging coils comprising first coil 142 and second coil 143 in someexamples, the recharging coil or coils located externally to a patient12 having an implanted IMD 15 according to the various examplesdescribed in this disclosure. In some examples, a single coil 142 may bea flat planar coil arranged to be placed proximate to, and in someexamples in direct contact with patient 12 in an area adjacent to IMD15. Single coil 142 may be electrically energized and configured toprovide a time-varying magnetic field that may be imposed on animplanted medical device, such as IMD 15 illustratively represented asbeing implanted in patient 12, for the purpose of recharging a powersource within the 1 MB. In some examples, coil 142 may be arranged as afirst coil of a pair of coils including a second coil 143, the pair ofcoils 142, 143 physically arranged so that when the coils areelectrically energized, a time-varying magnetic field is generatedbetween the coils that may be imposed on an implanted medical device,such as IMD 15, for the purpose of recharging a power source within the1 MB. In some examples, coils 142 and 143 may be physically arranged andelectrically configured as a Helmholtz coil. The arrangement of coil 142and/or coils 142 and 143 relative to patient 12 and IMD 15 as shown inFIG. 7 is not necessarily intended to be illustrative of the actualarrangement, for example with respect to positioning and/or scale of thecoil 142 or the pair of coils 142 and 143, and patient 12/IMD 15 duringa period of time when recharging of IMD 15 is occurring, and is intendedto be illustrative of various features of example system 140.

As shown in FIG. 7 , coil 142 (and coil 143 when provided), are coupledto recharging circuitry 141. Recharging circuitry 141 includes variouselectrical devices arranged to provide and to control the electricalenergization of coil 142, and/or coil pair 142/143, in order to generatea magnetic field that may be imposed onto IMD 15 when IMD is positionedproximate to coil 142 or between coil pair 142/143. In various examples,IMD 15 includes a receive antenna located within or coupled to the 1 MB,the receive antenna arranged as an example of any of the multi-axisantennas described in this disclosure, or any equivalents thereof. Themulti-axis antenna may be arranged to generate at least a minimum levelof induced current in one or more of the coils of the antenna regardlessof the direction of orientation of the magnetic field generated by coil142 and/or coils 142/143 imposed on IMD 15 and for a given PDL appliedto the IMD by the imposed magnetic field. As such, an elaborate systemof alignment equipment and/or additional and more complex coil alignmentprocedures may not be required in order to achieve an acceptable levelof inductive coupling efficiency between the magnetic field imposed onIMD 15 and the receive antenna of the IMD regardless of the orientationof IMD 15 relative to the direction of the imposed magnetic field.

For example, when recharging a power supply located within IMD 15 whileIMD 15 is implanted within patient 12, a single coil 142 may be placedin a position proximate to IMD 15 and external to patient 12, forexample covering and/or in contact with an area of patient 12, such asthe chest of the patient, adjacent to where 1 MB 15 has been implanted.IMD 15 in some examples may be considered to be a deeply implanteddevice, for example a device implanted within a chamber of the heart ofpatient 12. When positioned as described above, coil 142 may beenergized to generate a time-varying magnetic field that extends awayfrom coil 142 and is imposed onto IMD 15 and the multi-axis antennalocated within IMD 15. Because the receive antenna of IMD 15 is amulti-axis antenna, a precise alignment of the direction of the imposedmagnetic field relative to an orientation of IMD 15 and the receiveantenna is not critical or required, and may be a random relativeorientation. Despite this random relative orientation, at least aminimum level of recharging current may be induced into the receiveantenna of IMD 15 for a given level of PDL being provided by coil 142.The lack of a requirement for a precise or a particular alignmentbetween the magnetic field and the orientation of the IMD 15 may allowfor efficient and rapid recharging of the power source of the 1 MBwithout the need for a complex alignment procedure to be performed,and/or without the need for complex alignment apparatus to be providedand operated to align coil 142 and IMD 15. In some examples, simplypositioning coil 142 as a single coil proximate to the area of IMD 15,for example laying across an area of the chest of the patient 12 in thearea of implantation of IMD 15, is adequate to allow an efficient levelof inductive coupling between the magnetic field generated by coil 142and the multi-axis antenna of the IMD.

In a similar manner, when using a pair of coils 142 and 143 forrecharging a power source of IMD 15, the relative alignment of adirection of a magnetic field generated in the area between the coils142, 143 and the orientation of IMD 15 may not be critical with respectto achieving an efficient level of inductive coupling between themagnetic field and the receive antenna of the IMD. When IMD 15 ispositioned in the area between coil pair 142, 143, the coil pair may beenergized to generate a time-varying magnetic field extending betweenthe pair of coils, and that may be imposed onto IMD 15 and themulti-axis antenna located within IMD 15. Use of the coil pair 142, 143may provide a more uniform magnetic field throughout the area betweenthe coils, and thus further reducing or eliminating the need todetermine a particular positioning of IMD 15 relative to the position ofcoils 142, 143 while still providing an efficient level of inductivecoupling for inducing a recharging current into the receive antenna ofthe IMD. Further, because the receive antenna is this example is amulti-axis antenna, an alignment of the direction of the imposedmagnetic field generated between coil 142, 143 relative to anorientation of IMD 15 and the receive antenna may not be critical, andmay be a random relative orientation. Despite this random relativeorientation, at least a minimum level of recharging current may beinduced into the receive antenna of IMD 15 for a given level of PDLbeing provided by the pair of coils 142 and 143.

The lack of a requirement for a precise or a particular alignmentbetween the magnetic field generated by coil pair 142, 143 and theorientation of the IMD 15 may allow for efficient and rapid rechargingof the power source of the IMD without the need for a complex alignmentprocedure to be performed, and/or without the need for complex alignmentapparatus to be provided and operated to align coil pair 142, 143 andIMD 15. In some examples, simply positioning IMD 15 within the areabetween coils 142, 143, for example by positioning coils 142 and 143 onopposite sides of patient 12 so that the longitudinal axis common toboth coils aligns with IMD 15, is adequate to allow an efficient levelof inductive coupling between the magnetic field generated by the pairof coils 142, 143. and the multi-axis antenna of the IMD. The use of thepair of coils 142, 143 may further simply the requirement forpositioning of IMD 15 relative to the coil pair, and the relative levelof uniformity of the magnetic field provided between coils 142 and 143may allow for simply positioning the IMD somewhere in the area betweenthe coils, and energizing the coil pair to achieve an efficient level ofinductive coupling between the magnetic field and the receive antenna ofthe IMD.

Recharging circuitry 141 may be coupled to a computing device 146 thatincludes a display 146A and one or more input devices 146B, such as akeyboard and/or a computer mouse, that allow a user to interact withrecharging circuitry 141 through computing device 146. Computing device146 may be communicatively linked to recharging circuitry 141 by a wiredconnection 146C, and/or by a wireless connection 146D. In variousexamples, computing device 146 is configured to allow a user, such as aphysician or a technician (neither shown in FIG. 7 ), to operate andcontrol recharging circuitry 141 during a recharging session performedon IMD 15. Further, feedback received from IMD 15, for example receivedby computing device 146, may be used to control and adjust variousaspects of recharging circuitry 141, including adjusting the fieldstrength of the magnetic field being imposed on IMD 15, and controllingthe duration of the recharging process.

Feedback from IMD 15 in some examples comprises a value for the level ofcurrent that is being induced in the receive coil of IMD 15 through theinductive coupling of the energy being provided by coil 142, or by coilpair 142 and 143. Other information provided by IMD 15, such astemperature, rate of charge, and percentage of charge informationgenerated by IMD 15 may be transmitted from IMD 15 to computing device146 or other external devices, and use by recharging circuitry 141 tocontrol the energization of coils 142 and 143, and/or to determine whento terminate and/or regulate the power level being applied to therecharging process being performed by recharging circuitry 141 on IMD15.

System 140 further includes external computing devices, such as a server148 and one or more other computing devices 151A-151N, that may becommunicatively coupled to IMD 15, computing device 146, and/or externaldevice 144 via a network 147. In this example, IMD 15 may use itscommunication circuitry, at different times and/or in differentlocations or settings, to communicate with external device 144 via afirst wireless connection, and/or to communicate with an access point145 via a second wireless connection. In the example of FIG. 7 ,computing device 146, access point 145, external device 144, server 148,and computing devices 151A-151N are interconnected, and able tocommunicate with each other, through network 147.

Access point 145 may comprise a device that connects to network 147 viaany of a variety of connections, such as telephone dial-up, digitalsubscriber line (DSL), or cable modem connections. In other examples,access point 145 may be coupled to network 147 through different formsof connections, including wired or wireless connections. In someexamples, access point 145 may be co-located with the patient. Accesspoint 145 may interrogate IMD 15, e.g., periodically or in response to acommand from the patient or from network 147, to retrieve physiologicalmeasurements and/or other operational or patient data from IMD 15.Access point 145 may provide the retrieved data to server 148 vianetwork 147. In various examples, access point 145 may be any examplesof transceiver 16 described above.

In some cases, server 148 may be configured to provide a secure storagesite for data that has been collected from IMD 15, from rechargingcircuitry 141, and/or from external device 144. In some cases, server148 may assemble data in web pages or other documents for viewing bytrained professionals, such as clinicians, via computing devices151A-151N. The illustrated system 140 of FIG. 7 may be implemented, insome aspects, with general network technology and functionality similarto that provided by the Medtronic® CareLink® Network developed byMedtronic plc, of Dublin, Ireland.

In some examples, one or more of computing device 146, access point 145,server 148, or computing devices 151A-151N may be configured to perform,e.g., may include processing circuitry configured to perform, some orall of the techniques described herein, e.g., with respect to processingcircuitry of IMD 15 and external device 144, relating to the rechargingof power source located within IMD 15. In the example of system 140 asshown in FIG. 7 , server 148 includes a memory 149, which may beconfigured to store physiological and other data received from IMD 15and/or external device 144, and processing circuitry 150, which may beconfigured to provide some or all of the functionality ascribed toprocessing circuitry of IMD 15 as described herein. For example,processing circuitry 150 may provide programming and/or parameters thatare used by recharging circuitry 141 that may be used in the process ofproviding inductive recharging to a power source located within IMD 15.Configurations for and operational features of coil 142, coil pair 142and 143, and recharging circuitry 141 may be further described withrespect to FIGS. 8-11 of this disclosure.

FIG. 8 is a conceptual block diagram illustrating an example rechargingsystem 200 for recharging one or more implantable medical devicesimplanted in a patient 12 according to various examples described inthis disclosure. As illustrated, system 200 may be configured to provideinductive recharging of one or more implanted medical devices,illustratively represented as IMD 15, that are implanted in a patient,illustratively represented as patient 12. System 200 includes rechargingcircuitry 202 that is coupled to a single coil 212, or a pair of coils212, 215. The arrangement of coil 212 or the pair of coils 212 and 215relative to patient 12 and IMD 15 as shown in FIG. 8 is not necessarilyintended to be illustrative of the actual physical arrangement, forexample with respect to positioning and/or scale of the coil or the pairof coils and patient 12 and IMD 15 during a period of time whenrecharging of IMD 15 is occurring, and is intended to be illustrative ofvarious features of system 200. The actual arrangements of coil 212, orthe actual arrangement of coils 212 and 215 relative to each other, andrelative to patient 12 and IMD 15 may be as illustrated and describedwith respect to coils 142 and coil pair 142/143 as illustrated anddescribed with respect to FIG. 7 , and/or as further described belowwith respect to coils 212 and 215 as illustrated in FIG. 8 .

As illustrated in FIG. 8 , system 200 includes control circuitry 220coupled to recharging circuitry 202, and includes processing circuitry221, a memory 222 coupled to processing circuitry 221, for example bybus/connections 228 (herein after “bus 228”). Memory 222 may storeprogram instructions that, when retrieve and executed by processingcircuitry 221, provides programming steps that allow processingcircuitry 221 to control recharging circuitry 202 to perform therecharging processes associated with inductively recharging a powersource or power sources located within an IMD 15 implanted in patient12. In addition, memory 222 may also store values, for example chargingvalues, charging times, patient history associated specifically withpatient 12, communication protocols, and any other information that maybe required or that may be helpful to allow processing circuitry 221 tocontrol the inductive recharging process being used to recharge thepower source or sources included in IMD 15 when implanted within patient12 according to any of the techniques described in this disclosure, andany equivalents thereof.

Control circuitry 220 may include communication circuitry 224.Communication circuitry 224 may be used to receive and process signalsfrom the IMD 15 implanted in patient 12 for use by processing circuitry221 in controlling the inductive recharging processes including, but notlimited to a battery management system that monitors and optimizes therecharge process. Communication circuitry 224 may also provide wirelesscommunications with devices located externally to system 200, forexample external device 144, or for example external computing devices151A-151N, and/or external server 148 as described and illustrated withrespect to FIG. 7 . In FIG. 8 , communication circuitry 224 as may alsobe used to download information, such as programming information, tocontrol circuitry 220 that may then be stored in memory 222, andaccessed by processing circuitry 221.

As described above, memory 222 may be used to store information relatedto the recharging process performed by system 200, such as the levels ofenergy provided during a recharging process to coils 212 and/or coilpair 212 and 215, any fault conditions that have occurred during therecharging process, and any other information deemed necessary orhelpful that may be related to the recharging processes performed bysystem 200. This information as stored in memory 222 may be provided tocomputing device 230, and/or uploaded and transmitted throughcommunication circuitry 224 to some other external device or devices, asdescribed above. Control circuitry 220 as illustrated in FIG. 8 may alsoinclude sensor circuitry 223 configured to be coupled one more differentsensors 225, 226, and to receive signals from the sensors that may befurther processed by sensor circuitry 223 and/or by processing circuitry221, to provide and/or derive information that may be further used tocontrol and regulate the inductive recharging processes being performedby system 200.

In various examples, one or more of the circuits illustrated ascomprising control circuitry 220 may instead be provided by computingdevice 230. In various examples, computing device 230 includes a displayand one or more input devices, such as a keyboard and/or a computermouse, that allow a user, such as a physician or a clinician, tointeract with the system 200. This interaction may include interactionto control the recharging processes to be performed or being performedby system 200. In some examples, computing device 230 is computingdevice 146 as illustrated and described with respect to FIG. 7 , and isconfigured to provide some combination of or all of the featuresprovided by computing device 146, and to perform some combination or allof the functions ascribed to computing device 146. In some examples,control circuitry 220 and recharging circuitry 202 comprise some or allof recharging circuitry 141 as illustrated and described with respect toFIG. 7 , and may provide any of the features and be configured toperform any of the function ascribed to recharging circuitry 141.

As shown in FIG. 8 , recharging circuitry 202 includes a power supply203, a signal generator 204 (which may be comprised of an oscillator andsignal generation circuitry), one or more power amplifiers 210 and 213,and one or a plurality of corresponding matching network circuitry 211,214. The circuits of recharging circuitry 202 may be coupled by abus/connection 206. Bus 206 may be a same bus as bus 228, orcommunicatively coupled to bus 228. Recharging circuitry 202 includes afirst power amplifier 210 coupled to signal generator 204 and configuredto receive a signal from the signal generator 204. First power amplifier210 is also coupled to matching network circuitry 211, and configured toprovide an output signal to the matching network circuitry 211 based onthe signal received from the signal generator 204. Matching networkcircuitry 211 may be configured to provide impedance matching betweenpower amplifier 210 and coil 212, and to provide outputs that may becoupled to coil 212 to energize coil 212.

Recharging circuitry 202 in some examples includes a second poweramplifier 213 coupled to signal generator 204, and configured to receivea signal provided by signal generator 204. Second power amplifier 213 isalso coupled to matching network circuitry 214, and configured toprovide an output signal to the matching network circuitry 214 based onthe signal received from the signal generator 204. Matching networkcircuitry 214 is configured to provide impedance matching between poweramplifier 213 and coil 215, and to provide outputs that may be coupledto coil 215 to energize coil 215. In an alternative example, rechargingcircuitry 202 may include a second signal generator 205 that is coupledto the second power amplifier 213, wherein the second signal generator205 provides the input signal that is amplified by power amplifier 213and provided through matching network circuitry 214 to energize coil215. When the second signal generator 205 is utilized as part of system200, the second signal generator 205 may be configured to generate anoutput signal that is phase locked to the output signal generated by thefirst signal generator 204 so that the output signals provided by thefirst signal generator 204 and the second signal generator 205 are asame frequency signal and are in-phase with one another.

When system 200 is operating as a single coil recharging system, poweramplifier 210 may receive a signal including a waveform generated bysignal generator 204, and provide power amplification of the receivedsignal that is then applied through matching network circuitry 211 toenergize coil 212. In examples where system 200 is being operated usinga coil pair as the recharging coils, power amplifiers 210 and 213 mayreceive a signal including a waveform generated by signal generator 204,and provide power amplification of the received signal that is thenapplied through matching network circuitry 211, 214, respectively, toenergize coils 212 and 215. Matching network circuitry 211 and 214provides impedance matching between the output stage of the respectivepower amplifier that the matching network circuitry is coupled to andthe coil that is being energized by that particular power amplifier. Invarious examples, a typical range of impedance provided as an outputfrom one or more of power amplifiers 210, 213 may be in a range of 1 to100 ohms, in some examples 50 ohms, wherein the real part of the inputimpedance of the coils 212, 215 would be in a range of 0.1 to 20 ohms,in some examples 0.5 ohms. The imaginary part of a complex impedance ofthe coils may be in a range of 60 to several hundred ohms, depending onthe frequency of the signal or signal applied to the coils. In order toprovide maximum power transfer between the power amplifier outputs andthe respective coils these outputs are coupled to, the matching networkcircuitry 211, 214 are configured to match the impedance of the outputof the power amplifier to the coils each power amplifier is coupled tothrough the respective matching network circuitry.

In some examples, matching network circuitry 211, 214 comprise animpedance matching transformer configured to match an output impedanceof a power amplifier to an input impedance of a coil coupled to theoutput of the impedance matching circuitry. In some examples, matchingnetwork circuitry 211, and 214 comprises a transformer and/or acapacitor rated for peak voltage of the assembly and of a capacitancevalue that the inductive nature of the coil is accommodated. In oneimplementation, an adjustable vacuum ceramic capacitor is placed inseries with a 50Ω to 1Ω transformer. Other configurations and devicesmay be used to perform the impedance matching function of matchingnetwork circuitry 211 and 214, and are contemplated for using inproviding the matching network circuitry 211 and 214 as described inthis disclosure.

In various examples of system 200, since it is more difficult todynamically tune the quality factor of the receive antenna within animplanted medical device such as IMD 15, or rather, change the frequencyat which the quality factor is a maximum, it may significantly improvethe maximum power delivered to IMD 15 by fixing the frequency of thesystem based on the characteristics of the receive coils and using atunable vacuum capacitor located between the power amplifier (and aftera following transformer) and a coil 212 or a coil pair, such as coils212 and 215. This technique may be used in order to match the output ofthe power amplifiers to the impedance presented by the coils withoutchanging the oscillation frequency, as is practiced in otherrechargeable wireless power transfer systems such as the RestoreUltra®device from Medtronic plc, of Dublin, Ireland. A frequency basedmaximization configuration may result in a non-optimal power transfer ifthe secondary/receive coils of IMD 15 are tuned to a frequency differentthan that found to maximize power transfer to the primary/transmit coilsproviding the inductive energy provide by system 200. Therefore,examples of the systems and methods described herein comprise tuning theimpedance of the system at a fixed frequency, as opposed to varying thefrequency of the system, in order to maximize the power delivered to areceive coil in the implanted device being recharged by the system.

As shown in FIG. 8 , power supply 203 is coupled to a power input 201,and is configured to receive electrical power from power input 201.Power input 201 may be any source of electrical power, such ascommercially available electrical power supplied by an electricalutility, for example electrical power having 110-120 volts RMSsingle-phase power at a frequency of 50-60 Hz, as that is commonlyavailable in the United States. In other examples, power input 201 mayprovide power in other arrangements, such as but not limited to 480 voltthree-phase power in an ungrounded delta configuration at 50-60 Hz, or208 three-phase “Y” center grounded configuration at 50-60 Hz. Othervoltages, frequencies, configurations, and numbers of phases arecontemplated for use as the power input 201 to system 200, as would beunderstood by one of ordinary skill in the art. Power supply 203 isconfigured to receive electrical power from power input 201, and mayperform various operations on the received electrical power, includingconditioning, filtering, and conversion of the input power voltage toone or more different voltages, including both different voltagesprovided as alternating current (AC) voltage supplies and direct current(DC) power supplies as outputs from power supply 203. These poweroutputs are generally represented by the “TO OTHER CIRCUITRY” outputarrow illustratively provided as an output from power supply 203, andmay include any electrical power outputs required to power the circuitryfor operation of the devices included in and powered from system 200.

In some examples, power supply 203 is also configured to provide one ormore separate outputs, illustratively represented by the “TO POWERAMPLIFIERS” output arrow from power supply 203. These outputs from powersupply 203 may be directly coupled to power amplifiers 210 and 213provided as part of recharging circuitry 202, and wherein the “TO POWERAMPLIFIERS” output is configured to provide the electrical energy usedto energize the coil 212 and/or coil pair 212, 215 under the control ofthe power amplifiers 210 and 213, respectively.

In FIG. 8 , signal generator 204 is coupled to bus 206, wherein signalgenerator 204 may be configured to generate one or more output signalsthat are used to control the waveforms of the electrical power used toenergize coil 212 and/or coil pair 212, 215. For example, signalgenerator 204 may generate a signal having sinusoidal voltage waveformand a particular frequency. This signal is provided to the poweramplifier(s) and matching network circuitry of recharging circuitry 202.In some examples, the sinusoidal waveform is converted to a squarewaveform, the frequency of the square waveform having a same frequencyof the sinusoidal waveform generated by signal generator 204, or inother examples signal generator 204 may change the frequency of thesquare waveform signal. In some examples, the duty cycle of the squarewave may be the same as provided with the sinusoidal waveform (e.g., a50% duty cycle), and in other examples, signal generator 204 may alterthe duty cycle to a duty cycle other than a 50% duty cycle for thesquare waveform signal.

In some examples, signal generator 204 amplifies the signal for exampleto alter the voltage level of the signal. In some examples, signalgenerator 204 is configured to process the signal to retain theprocessed signal as a sinusoidal waveform, but for example acts as abuffer or driver to amplify and/or drive the output signal from thesignal generator 204 to the power amplifier 210 and/or amplifiers 210and 213, and for example to prevent the power amplifiers from loadingdown or otherwise distorting the signal being provided from the signalgenerator 204. In some examples, one or more of the power amplifierscomprise a Class D amplifier. In some examples, one or more of the poweramplifiers comprise a Class E amplifier. In some examples, the signalgenerator 204 may provide recharge frequency tuning (closed loop or openloop), to optimize the wireless power transfer between coil 212 or coilpair 212, 215 and the receive antenna of IMD 15. This tuning may or maynot be integrated and coordinated with the battery management system andtelemetry/communication systems.

Once processed by signal generator 204, the signal generator 204 iscoupled to power amplifier 210 that is configured to control the outputof electrical energy provided by matching network circuitry 211 to coil212 using the signal processed by signal generator 204, which may beprovided by a coupling the power amplifier 210 to the “TO POWERAMPLIFIER” output of power supply 203. The output from power amplifier210 is then provided as an output to matching network circuitry 211 toenergize coil 212. Matching network circuitry 211 may also include afeedback 211A loop that provides a feedback signal, such as a varyingvoltage level, that is indicative of the level of energy, for example acurrent flow, being provided to coil 212 by matching network circuitry211. This feedback signal may be processed by one or more devicesincluded in system 200, for example processing circuitry 221 orcomputing device 230, or other battery management systems, to provideinformation that may be used to control and regulate the output ofelectrical energy being provided to energize coil 212. Energization ofcoil 212 may provide a magnetic field, generally indicated by arrows217, that extend away from coil 212, for example in a direction defininga direction for the magnetic field.

When operating system 200 as a single recharging coil system, electricalenergy may be provided to only coil 212, and coil 215 may not beprovided as part of system 200. When energizing coil 212 as a singlerecharging coil system, coil 212 may be a flat planar coil having aspiral wound coil configuration. In some examples, the flat planar coilmay include an electrical conductor, such as 4500/48 Litz wire, forming20 turns extending in a flat spiral shaped arrangement and having adiameter of approximately 50 centimeters. In some examples, the flatplanar coil may include an electrical conductor, such as 105/40 Litzwire, forming 12 turns of the conductor extending in a flat spiralshaped arrangement and having a diameter of approximately 30centimeters. Other variations in the types of wire, the number of turns,and/or the diameter of the coils may be used, and are contemplated foruse in the single coils systems of system 200. For example, 4500/48 Litzwire may also be used to form the 30-centimeter diameter coil.

In examples using a single planar recharging coil for coil 212, thedirection (e.g., the angle) of magnetic field 217 relative to coil 212may vary based on the distance and position from the coil. For example,portions of the magnetic field closest to coil 212 may have a magneticfield direction that is generally perpendicular to the coil, andparallel to longitudinal axis 218 of the coil. As the distance from coil212 increases, the direction of magnetic field may change, and varythrough a range of angles relative to the surface of the coil 212 andrelative to longitudinal axis 218 so that at some distance from the coilthe direction of the magnetic field is parallel to the surface of thecoil 212 and is perpendicular to the longitudinal axis 218. When an IMDsuch as IMD 15 is placed adjacent to coil 212, for example by placingcoil 212 on an exterior surface of patient 12 in the area where IMD 15is implanted, the direction of the portion of the magnetic field that isimposed on the IMD, and thus on the receive antenna within the IMD, isvariable based for example on the depth of the implanted device withinthe patient and thus the distance of the receive antenna from thesurface of the coil 212. As described above, the multi-axis antenna ofIMD 15 is configured to provide at least a minimum level of inducedrecharging current for a given power level of the imposed magnetic fieldregardless of the orientation of the direction of the magnetic fieldrelative to the orientation of the receive antenna. As such, aneffective level of inductive coupling may be achieved between themagnetic field generated by coil 212 and the receive antenna of IMD 15during a recharging session by simply placing coil 212 on or near theexternal surface of patient 12 in the area of implantation of IMD 15without the need for complex alignment procedures to be performed andwithout the need for complex apparatus to align the position and/orangular orientation of coil 212 relative to patient 12 and IMD 15.

When operating system 200 using the coil pair 212, 215, signal generatormay provide a signal to power amplifier 210 to energize coil 212 throughmatching network circuitry 211 as described above. In addition, signalgenerator 204 may also provide a signal to power amplifier 213, whichreceives power from the “TO POWER AMPLIFIERS” output from power supply203, and provides an output to matching network circuitry 214 toelectrically energize coil 215. Power amplifier 213 and matching networkcircuitry 214 may be configured to operate and to provide any of thefeatures and functions described above with respect to power amplifier210 and matching network circuitry 211, respectively, in providing theelectrical energy used to energize coil 215. In addition, matchingnetwork circuitry 214 includes a feedback signal 213A, that may be usedin same or similar matter as described above with respect to feedbacksignal 211A, but for use in controlling and regulation of poweramplifier 213 and the matching network circuitry 214 with respect toproviding the electrical energy used to energize coils 215.

In various examples, the same signal is provided by signal generator 204to both power amplifier 210 and to power amplifier 213. The poweramplifiers 210, 213 may then process the signal and control matchingnetwork circuitry 211 and 214, respectively, so that a same level ofelectrical energy is provided to both sets of coils 212 and 215 at anygiven time when coils 212 and 215 are energized. The polarity of theelectrical power provided to coils 212 and 215 may be arranged such thatthe coils generate a generally uniform resultant magnetic fieldthroughout the area 216 between the coils, the resultant magnetic fieldgenerally indicated by arrows 217. For example, coils 212 and 215 may bephysically constructed and arranged relative to one another to form aHelmholtz coil. A Helmholtz coil in some examples consists of a pair ofcoils, each coil having a circular-shaped winding encircling a portionof a longitudinal axis such as axis 218 that is common to both coils,each of the coil windings generally formed in a plane or a set of planesthat are perpendicular to the longitudinal axis, the coils havingwindings that are themselves coplanar to each other and separated by adistance along the longitudinal axis that is equal to a value for theradius of each of the circular-shaped coil winding.

In some examples, the resultant magnetic field formed in area 216between coil pair 212 and 215 may have a magnetic field direction thatis generally parallel with longitudinal axis 218 throughout the area216, and having an orientation that extends from coil 212 toward coil215 or that extends from coil 215 toward coil 212 depending on thepolarity of the electrical energy applied to each coil. Because themagnetic field intensity and the direction of the magnetic field in thearea 216 is generally consistent throughout area 216, the precisepositioning of patient 12 and IMD 15 between coils 212, 215 is notcritical, and positioning patient 12 so the IMD 15 is located withinarea 216 may be sufficient to impose the magnetic field onto the receiveantenna of IMD 15 so that efficient inductive coupling may be achievedbetween the magnetic field and the receive antenna.

As described above, the multi-axis antenna of IMD 15 is configured toprovide at least a minimum level of induced recharging current for agiven power level of the imposed magnetic field regardless of theorientation of the direction of the magnetic field relative to theorientation of the receive antenna. As such, an effective level ofinductive coupling may be achieved between the uniform magnetic fieldgenerated by the coil pair 212, 215 and the receive antenna of IMD 15during a recharging session by simply placing IMD 15 within area 216between coils 212 and 215 without the need for complex alignmentprocedures to be performed, and without the need for complex apparatusto align the position and/or angular orientation of coil pair 212, 215relative to patient 12 and IMD 15.

In operation, a patient 12 with at least one IMD 15 that requiresrecharging of the power source located within the at least one IMD 15 ispositioned so that the IMD 15 is located within the area of the magneticfield that will be generated by coil 212 when operating system 200 as asingle recharging coil configuration, or so that IMD 15 is locatedwithin the area between coils 212 and 215 when operating system 200using a pair of recharging coils. Based on control provided byprocessing circuitry 221 and/or by instructions received from computingdevice 230, signal generator 204 generates one or more signals that areprovided to the power amplifier 210 and/or amplifiers 210 and 213. Thepower amplifier(s), based at least in part on the received signal, andin some examples based on instructions received from processingcircuitry 221, provide power outputs to energize coil 212 or the pair ofcoils 212 and 215. When energized, the coil(s) generate a magnetic field(or a resultant magnetic field) that that is imposed onto the receiveantenna of IMD(s) 15, which begins to provide inductive charging currentto the power source located in IMD 15. Signals either provided by IMD 15to communication circuitry 224 and/or signals provided as feedbacksignal(s) 211A, and 213A, are processed, for example by processingcircuitry 221, and may be used to regulate the energy levels applied tothe coil 212 or the coil pair 212, 215.

During the process of inductively recharging the power source located inIMD 15, various sensors 225, 226, may be monitored, and the informationreceived from or derived from the sensors may be used to further controlthe recharging process. For example, temperature sensors located at thecoils may provide signals indicative of the temperatures of coils 212,215, and may be monitored during the recharging process to determine ifone or more of the coils may be overheating. In some examples, one ormore of sensors 225, 226 may sense a magnetic field strength and/ordirection of the resultant magnetic field at one or more locations inthe area proximate to coil 212 or the area 216 between coils 212 and215. The information from the one or more sensors 225, 226 may bereceived at sensor circuitry 223, and may be further processed, forexample by processing circuitry 221, and used as a further basis forcontrol of the recharging process being performed by system 200. Forexample, the level of the intensity of the magnetic field beinggenerated by coil 212 or coil pair 212 and 215 as sensed by the one ormore sensor 225, 226 and may be monitored to assure that a safe level ofexposure to the electromagnetic fields provided to the patient 12 aremaintained.

In some examples, a temperature of the patient 12 and/or of IMD 15 maybe monitored during the recharging process. These sensed temperatures ofpatient 12 and/or of IMD 15 may be used to control the rechargingprocess for example by lowering (reducing) the level of energy beingprovided to the coils if the temperature of the patient 12 or of IMD 15is rising, and for example shutting off the energy or lowering theenergy level being provided to the coil or pair of coils if thetemperature of the patient 12 or of IMD 15 exceeds a temperatureconsidered to be safe for the patient. Further, the strength of themagnetic field being generated and imposed on IMD 15 may be monitoredduring the recharging process, and the sensed strength of the magneticfields may be processed and used to further regulate the process, forexample to raise or lower the level of electrical energy being providedto the coils. Monitoring of the strength of the magnetic field imposeson the patient 12 may be required to assure that the level of thestrength of the magnetic field does not exceed a predetermined level, ora predetermined level for more than a predetermined time period. Themonitoring may include a reduction, including lower the energy level orshutting off the electrical energy provided to the coils for safetyreasons if the strength of the magnetic field exceeds some predeterminedvalue or values, either instantaneous and/or over some predeterminedtime period.

In various examples, processing circuitry 221 regulates variousfunctions related to the recharging process. Processing circuitry 221may include a timer function for controlling and limiting the durationof time the patient 12 may be exposed to the magnetic fields beinggenerated by coil 212 or coil pair 212, 215 during the rechargingprocess. Timing functions may be provided by one or more timers includedin processing circuitry 221, and may timeout based on one or more timervalues stored in memory 222. Processing circuitry 221 may also regulatea profile of the levels of electrical energy provided to the rechargingcoil or coil pair over the duration of the recharging process, so thatthe levels of electrical energy provided to coil 212 or to each of thecoils 212 and 215 may be set and/or varied over the duration of therecharging process based on a profile that may be stored in memory 222and retrieved and executed by processing circuitry 221.

In some examples, IMD 15 may provide a signal (e.g., wireless signal227) to communication circuitry 224 that indicates the level of rechargethat has been provided to the power source within IMD 15. Processingcircuitry 221 may further regulate and/or terminate the rechargingprocess of IMD 15 based on this information. For example, a wirelesssignal 227 provided by IMD 15 may indicate that the power source locatedwithin IMD 15 is fully recharged, and further exposure to the magneticfields by both patient 12 and IMD 15 will provide no further charging ofthe power source. In such instances, processing circuitry 221 mayterminate the recharging process in order to minimize the amount ofexposure of patient 12 to the magnetic fields generated by system 200,regardless of whether or not a timer has indicated that the time forrecharging the power source of IMD 15 has expired.

FIG. 9 illustrates graphs 250, 260 of representative waveforms 251, 261that may be generated by a signal generator and applied to therecharging coil or coils of a recharging system according to variousexamples described in this disclosure. The representative waveforms 251,261 may be generated by a signal generator, such as signal generator 204and/or signal generator 205 as illustrated and described with respect toFIG. 8 , and applied to the coil (e.g., coil 142 of FIG. 7 ; coil 212 ofFIG. 8 ), or a pair of coils (e.g., coils 142 and 143 of FIG. 7 ; coils212 and 215 of FIG. 8 ) coupled to recharging circuitry according tovarious examples described in this disclosure. In FIG. 9 , graph 250illustrates the example waveform 251 of a square wave having anamplitude value plotted against the vertical axis 252 over time, timerepresented by horizontal axis 253. Waveform 251 comprises apeak-to-peak amplitude 254, and a cycle period 255. In various examples,the peak-to-peak amplitude 254 of waveform 251 may comprise a voltagerange of 10 mV to 100 volts, in some examples, 5 volts. The peak-to-peakamplitude in some examples is dependent on the power amplifier selectedthat the waveform 251 is being provided to in order to generate theoutput used to energize one coil or a pair of electrical coils arrangedas recharging coils in a recharging system.

In some examples, the power amplifier being driven by the waveform 251is a fixed amplification power amplifier, capable of providing a400-Watt output signal based on a variable input signal having apeak-to-peak amplitude 10-200 mV. In some examples, a reference voltagelevel 256 may comprise a zero-volt reference voltage, wherein a portionof waveform 251 is provided at voltage level that is a higher voltagethan the reference voltage 256, and a portion of waveform 251 isprovided at a voltage level that is less than the reference voltagelevel 256. In various examples, the duty cycle of waveform 251 overperiod 255 provides a fifty-percent duty cycle. In various examples, theduty cycle of waveform 251 over the period 255 provides a duty cycleother than a fifty-percent duty cycle. In various examples the timeperiod 255 of waveform 251 is in a range of 100 microseconds to 100nanoseconds, representative of a frequency range of 10 kHz to 10 MHz forwaveform 251.

In some examples, an electrical voltage having a waveform correspondingto waveform 251 may be applied to a single recharging coil to generate amagnetic field that may be imposed on a multi-axis antenna of animplanted medical device to induce a recharging current into the antennafor the purpose of recharging a power source of the implanted medicaldevice. The multi-axis antenna may be any of the examples of themulti-axis antenna described throughout this disclosure configured toprovide at least a minimum level of recharging current for a givenenergy level associated with the imposed magnetic field regardless ofthe orientation of the direction of the magnetic field generated by thesingle recharging coil relative to the orientation of the implantedmedical device and the multi-axis antenna.

In some examples, an electrical voltage having a waveform correspondingto waveform 251 may be applied to a pair of coils to generate agenerally uniform magnetic field between the pair of coils that may beimposed on a multi-axis antenna of an implanted medical devicepositioned in an area between the pair of coils. The uniform magneticfield may be used to induce a recharging current into the multi-axisantenna for the purpose of recharging a power source of the implantedmedical device. The multi-axis antenna may be any of the examples of themulti-axis antenna described throughout this disclosure configured toprovide at least a minimum level of recharging current for a givenenergy level associated with the imposed magnetic field regardless ofthe orientation of the direction of the uniform magnetic field generatedby the pair of coils relative to the orientation of the implantedmedical device and the multi-axis antenna.

In some examples, electrical energy having the same electricalparameters such as amplitude, duty cycle, and phase for waveform 251 isapplied to each of the pair of coils being utilized as the rechargingcoils. Other and/or different combinations of differences between theelectrical parameters of waveform 251 applied to the first electricalcoil and at a same time to the second electrical coil is not limited tovariation of the amplitude 254 of the waveforms, and may include othervariation, such as differences in the duty cycle of the waveformsapplied for example to the first coil compared to a duty cycle of thewaveform that is applied to the second electrical coil.

Graph 260 illustrates an example waveform 261 of a sinusoidal waveformhaving a varying amplitude value plotted against the vertical axis 262over time, time represented by horizontal axis 263. Waveform 261comprises a peak-to-peak amplitude 264, and having a period 265. Invarious examples, the peak-to-peak amplitude 264 of waveform 261 maycomprise a voltage range of 10 mV to 100 volts, in some examples, 5volts. The peak-to-peak amplitude in some examples is dependent on thedesired peak magnetic field intensity and the capacity of the poweramplifier employed. In some examples, the power amplifier being drivenby waveform 261 is a fixed 400-Watt power amplifier, in other examplethe power amplifier comprises a variable output between 2 Watt and 1 kW.In some examples, a reference voltage level 266 may comprise a zero-voltreference voltage, wherein a portion of waveform 261 provides a voltagelevel above the reference voltage level 266, and another portion of eachcycle of waveform 261 comprises voltage value that is below thereference voltage level 266. In various examples, the duty cycle ofwaveform 261 over period 265 provides a fifty-percent duty cycle ofvoltage levels above the reference voltage level 266. In variousexamples the time period 265 of waveform 261 is in a range of 100microseconds to 100 nanoseconds, representative of a frequency range of10 kHz to 10 MHz for waveform 261.

In some examples, an electrical voltage having a waveform correspondingto waveform 261 may be applied to a single recharging coil to generate amagnetic field that may be imposed on a multi-axis antenna of animplanted medical device to induce a recharging current into the antennafor the purpose of recharging a power source of the implanted medicaldevice. The multi-axis antenna may be any of the examples of themulti-axis antenna described throughout this disclosure configured toprovide at least a minimum level of recharging current for a givenenergy level associated with the imposed magnetic field regardless ofthe orientation of the direction of the magnetic field generated by thesingle recharging coil relative to the orientation of the implantedmedical device and the multi-axis antenna.

In some examples, an electrical voltage having a waveform correspondingto waveform 261 may be applied to a pair of coils to generate agenerally uniform magnetic field between the pair of coils that may beimposed on a multi-axis antenna of an implanted medical devicepositioned in an area between the pair of coils. The uniform magneticfield may be used to induce a recharging current into the multi-axisantenna for the purpose of recharging a power source of the implantedmedical device. The multi-axis antenna may be any of the examples of themulti-axis antenna described throughout this disclosure configured toprovide at least a minimum level of recharging current for a givenenergy level associated with the imposed magnetic field regardless ofthe orientation of the direction of the uniform magnetic field generatedby the pair of coils relative to the orientation of the implantedmedical device and the multi-axis antenna.

In some examples, electrical energy having the same electricalparameters such as amplitude, duty cycle, and phase for waveform 261 isapplied to each of the pair of coils being utilized as the rechargingcoils. Other and/or different combinations of differences between theelectrical parameters of waveform 261 applied to the first electricalcoil and at a same time to the second electrical coil is not limited tovariation of the amplitude 264 of the waveforms, and may include othervariation, such as differences in the phases of the waveforms appliedfor example to the first coil compared to the second coil.

FIG. 10 is a flowchart illustrating a method 300 according to variousexamples described in this disclosure. Method 300 includes recharging apower source located in an implanted medical device implanted within apatient. Method 300 is described as being performed by system 200 asillustrated and described with respect to FIG. 8 , the rechargingprocess performed on implantable medical device 30 having a multi-axisantenna 40 located within the device as illustrated and described withrespect to FIG. 2 . However, method 300 is not limited to beingperformed examples of system 200 performing the recharging process on animplanted medical device, and method 300 is not limited to rechargingprocesses performed on examples of device 30. Other devices havingexamples of the multi-axis receive antennas as described throughout thisdisclosure, and any equivalents thereof, that are configured to haverecharging currents induced into the antenna for the purpose ofrecharging a power source of the implanted medical device arecontemplated by the processes of method 300.

Method 300 includes a recharging circuitry 202 of system 200 energizingat least one recharging coil, e.g., coil 212 or a pair of coils 212,215, to generate a magnetic field 217 (block 302). In instances wherethe recharging coil is a single recharging coil, such as coil 212, therecharging coil may be a flat planar coil according to any of theexamples described throughout this disclosure. In instances where therecharging coil is a pair of coils, such as coils 212 and 215, the pairof coils may be physically arranged and electrically energized accordingto any of the pairs of coils described throughout this disclosure,including coils 212 and 215 arranged to form a Helmholtz coil.

Method 300 includes imposing the generated magnetic field onto amulti-axis (receive) antenna 40 of the implanted medical device 30having a rechargeable power source, such as battery 39, that is to berecharged (block 304). In some examples where a single recharging coilis being utilized to generate the magnetic field, imposing the magneticfield onto the multi-axis antenna may include placing the rechargingcoil proximate to, and in some examples in contact with, an exteriorarea or surface of the patient having the implanted medical device to berecharged adjacent to the location of the implanted device. In someexamples where a pair of coils is being utilized to generate themagnetic field, imposing the magnetic field onto the multi-axis antennamay include positioning the patient, and thus the implanted medicaldevice 30, within an area located between the pair of coil 212, 215. Themulti-axis antenna of the implanted device may include any of theexamples of multi-axis antenna, such as antenna 89 as illustrated anddescribed with respect to FIG. 4 , which may be positioned within, e.g.,encircled by an antenna window 42 of device 30 as illustrated anddescribed with respect to FIG. 2 . In various examples, the multi-axisantenna includes a ferrite core that is encircled, at least partially,by each of the coil windings forming the antenna 89.

Method 300 includes summing, by recharging circuitry, one or moreelectrical currents induced into one or more of the coils of themulti-axis antenna to generate a recharging current (block 306). Summingthe induced electrical currents to may include coupling each of thecoils of the multi-axis antenna to an individual diode, such as diodes54, 57, and 60 as illustrated and described with respect to schematicdiagram 50 and FIG. 3 . In various examples, summing the inducedelectrical currents may include filtering the current or currentsgenerated in one or more of the coils of the multi-axis antenna usingone or more capacitors, such as capacitor 61 as illustrated anddescribed with respect to schematic diagram 50 and FIG. 3 .

Referring to FIG. 10 , method 300 includes applying, by rechargingcircuitry, the generated recharging current to the power source, such asbattery 39, of the implanted medical device 30 (block 308). In variousexamples, applying the recharging current to the power source includescontrolling the coupling of the recharging current to a power source,such as power source 62, through a switching device, such as switchingdevice 92, the switching device controlled by recharging circuitry, suchas recharging circuitry 90 as illustrated and described with respect toschematic diagram 50 and FIG. 3 .

FIG. 11 is a flowchart illustrating a method 320 according to variousexamples described in this disclosure. Method 320 includes a method formanufacturing a multi-axis antenna for an implanted medical device thatis to be implanted within a patient. Method 320 is described asmanufacturing an implantable device 30 designed to be implanted within achamber of the heart of a patient, and to include a multi-axis antennaconfigured to generate a recharging current when a magnetic field isimposed on the antenna, the recharging current for recharging a powersource (e.g., battery 39) of the device 30. However, method 320 is notlimited to manufacturing the implantable medical device 30 having themulti-axis antenna as illustrated and described for example with respectto FIG. 2 , and may be applied to the manufacture of a variety ofimplantable medical devices having a multi-axis antenna according to theexamples of multi-axis antenna and implantable medical devices asdescribed throughout this disclosure, and any equivalents thereof.

Method 320 includes forming a core 85 for the multi-axis antenna (block322). Core 85 in some examples is formed from a ferrite material. Insome examples, the core 85 is formed to have a cubic shape having a samevalue for a height, a width, and a depth dimension of the core. Core 85in some examples has a value for each of the height, width, and depthdimension of three millimeters, having a total volume for the core oftwenty-seven cubic millimeters.

Method 320 includes forming a first coil 71 comprising a windingencircling the core (block 324). The first coil winding may be formed ofan electrically conductive wire, such as Litz wire. The first coilwinding may be formed to include an interior space, the winding formedto encircle the core so that the core is at least partially includedwithin the interior space of the first coil winding. First coil windingmay encircle a first coil axis of orientation forming a normal axis forthe first coil. The first coil winding may encircle the core so that thefirst coil winding extends along the outer surfaces of the core alongtwo of the three dimensions of the core.

Method 320 includes forming a second coil 80 comprising a windingencircling the core and encircling the first coil winding (block 326).The second coil winding may be formed of an electrically conductivewire, such as Litz wire. The second coil winding may be formed toinclude an interior space, the winding formed to encircle the core sothat the core is at least partially included within the interior spaceof the second coil winding. The second coil winding may encircle asecond coil axis of orientation forming a normal axis for the secondcoil, the second coil axis of orientation orthogonal to the first coilsaxis of orientation. The second coil winding may encircle the core sothat the second coil winding extends along the outer surfaces of thecore along two of the three dimensions of the core, at least one of thetwo dimensions that is different from the two dimensions encircled bythe first coil winding.

Method 320 includes forming a third coil 76 comprising a windingencircling the core, encircling the first coil winding, and encirclingthe second coil winding to form an antenna assembly (block 328). Thethird coil winding may be formed of an electrically conductive wire,such as Litz wire. The third coil winding may be formed to include aninterior space, the winding formed to encircle the core so that the coreis at least partially included within the interior space of the thirdcoil winding. The third coil winding may encircle a third coil axis oforientation forming a normal axis for the third coil, the third coilaxis of orientation orthogonal to both the second coil axis oforientation and the first coils axis of orientation. The third coilwinding may encircle the core so that the third coil winding extendsalong the outer surfaces of the core along two of the three dimensionsof the core, at least one of the two dimensions that is different fromone of the two dimensions of the core encircled by the first coilwinding, and at least one of the two dimensions encircled by the thirdcoil winding different from one of the two dimensions of the coreencircled by the second coil winding.

Method 320 includes electrically coupling the antenna assembly torecharging circuitry (block 330). Electrically coupling the antennaassembly to recharging circuitry may include coupling each of the firstcoil winding, the second coil winding, and the third coil winding toindividual diodes configured to rectify the current induced,respectively, in each of the coils. The recharging circuitry may beconfigured to sum any current or current induced into any of the firstcoil winding, the second coil winding, and/or the third coil winding togenerate a recharging current. In various examples, the antenna assemblyis not orientation specific with respect to a direction of the magneticfield that may be imposed onto the antenna assembly of the purpose ofgenerating the recharging current in the antenna assembly. Because theaxis of orientation of each of the windings of the coils of themulti-axis antenna are orthogonal to each other, the multi-axis antennamay be configured to produce a level of recharging current that is atleast a minimum level of current that could be provided by any of thecoils under a maximum coupling efficiency for that coil, the multi-axisantenna configured to provide the minimum level of current regardless ofthe orientation of a magnetic field imposed on the antenna assemblyrelative to the orientation of the antenna assembly.

Method 320 includes positioning the antenna assembly within a housing ofthe implantable medical device (block 332). In various examples, theantenna assembly is positioned within the housing so that an antennawindow portion of the housing encircles, (e.g., at least partiallysurrounds), the antenna assembly. In some examples, the antenna windowis made from a material, such as sapphire, that is highly radiofrequency transmissive. In some examples, the antenna window is madefrom a material that is a different material used to form a firsthousing portion and/or a second housing portion of the housing of theimplantable medical device. In various examples the antenna window isformed of a material that allows magnetic fields having frequencies in arange of 10 kHz to 100 MHz to be transmitted through the antenna windowfor outside the housing of the implantable medical device and be imposedonto the antenna assembly positioned within the housing with no or avery little level of attenuating of the strength of the magnetic field.

Although the examples of a multi-axis antenna have generally beendescribed in this disclosure as having three individual coils, examplesof a multi-axis antenna that may be incorporated into an implanteddevice are not necessarily limited to antenna comprising three coils. Amulti-axis antenna may include an antenna that is made from two coilsforming parallel connected coils arrange in such a way to provide anefficient level of inductive coupling for certain orientations of thedirection of an imposed magnetic field directed toward the deviceincluding the two-coil antenna, such as a window 42 of device 30 asillustrated and described with respect to FIG. 2 . A multi-axis antennamay also be formed using one or more serially connected or continuouslywound coils that forms a curved coil arranged inside curvature of windowof a device, such as window 42 of device 30 as shown and described withrespect to FIG. 2 .

Further, use of the devices, systems, and techniques described in thisdisclosure are not limited to use in devices only during rechargingsessions applied to the devices. An example of a multi-axis antenna asdescribed throughout this disclosure, or any equivalent thereof, may beincluded a part of a passive device. In some examples, the passivedevice may not include an internal power source capable of storingelectrical energy, and may only operate when energized from an externalpower source, for example by receiving power from an external devicethrough inductively coupled electrical energy provided by the externaldevice. When operating a passive device, an external device that mayinclude a transmit coil arranged to be electrically energized togenerate a magnetic field that is imposed on the multi-axis antenna ofthe passive device. The imposed magnetic field generates one or morecurrents in the multi-axis antenna of the passive device, and additionalcircuitry of the passive device is arranged to receive these inducedcurrents to electrically power and operate the passive device. Thesecurrent(s) inducted into the multi-axis antenna may be referred to as“operating current” because they are used to electrically power andoperate the passive implantable medical device.

Once powered by the induced currents, the implanted medical device mayperform a variety of functions, including sensing physiologicalparameter associated with a patient in order to monitoring and/ordiagnose a condition of the patient, and/or to provide therapy, such aselectrical stimulation therapy, to the patient while the passive deviceis being powered through the imposed magnetic field. The need to operatethe passive device in some instances may only require that the device bepowered for a short interval of time, for example for a thirty-minutetime period and only periodically, for example once daily, or in otherexamples one time per week or once monthly. By eliminating the need tohave a power source located within or as part of the passive device, theoverall size and/or the dimension of the passive device may be reducedrelative to a similar device that includes a power source included aspart of the device. The smaller size for the passive device may allow aless intrusive implantation to implant the passive device at theimplantation site, and may contribute to patient comfort followingimplantation of the device due to the smaller size of the implanteddevice.

The techniques of this disclosure may be implemented in a wide varietyof computing devices, medical devices, or any combination thereof. Anyof the described units, modules or components may be implementedtogether or separately as discrete but interoperable logic devices.Depiction of different features as modules or units is intended tohighlight different functional aspects and does not necessarily implythat such modules or units must be realized by separate hardware orsoftware components. Rather, functionality associated with one or moremodules or units may be performed by separate hardware or softwarecomponents, or integrated within common or separate hardware or softwarecomponents.

The techniques described in this disclosure may be implemented, at leastin part, in hardware, software, firmware or any combination thereof. Forexample, various aspects of the techniques may be implemented within oneor more microprocessors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs), or any other equivalent integrated or discrete logic circuitry,as well as any combinations of such components, embodied in programmers,such as physician or patient programmers, stimulators, or other devices.The terms “processor,” “processor circuitry,” “processing circuitry,”“controller” or “control module” may generally refer to any of theforegoing logic circuitry, alone or in combination with other logiccircuitry, or any other equivalent circuitry, and alone or incombination with other digital or analog circuitry.

For aspects implemented in software, at least some of the functionalityascribed to the systems and devices described in this disclosure may beembodied as instructions on a computer-readable storage medium such asrandom-access memory (RAM), read-only memory (ROM), non-volatilerandom-access memory (NVRAM), electrically erasable programmableread-only memory (EEPROM), FLASH memory, magnetic media, optical media,or the like that is tangible. The computer-readable storage media may bereferred to as non-transitory. A server, client computing device, or anyother computing device may also contain a more portable removable memorytype to enable easy data transfer or offline data analysis. Theinstructions may be executed to support one or more aspects of thefunctionality described in this disclosure.

In some examples, a computer-readable storage medium comprisesnon-transitory medium. The term “non-transitory” may indicate that thestorage medium is not embodied in a carrier wave or a propagated signal.In certain examples, a non-transitory storage medium may store data thatcan, over time, change (e.g., in RAM or cache).

Various aspects of this disclosure have been described. These and otheraspects are within the scope of the following claims.

What is claimed is:
 1. A method comprising: receiving, at a multi-axisantenna of a medical device internal to a patient, a magnetic fieldhaving a magnetic field direction, the magnetic field generated by atleast one recharging coil, wherein the magnetic field induces one ormore electrical currents in one or more of a plurality of coils formingthe multi-axis antenna, the plurality of coils comprising a first coilhaving a first coil axis of orientation, a second coil having a secondcoil axis of orientation, and a third coil having a third coil axis oforientation; rectifying the one or more electrical currents induced inthe one or more plurality of coils; summing the one or more rectifiedelectrical currents to form a recharging current; applying therecharging current to a power source of the medical device to rechargethe power source; and switching, with a switching device, the summed oneor more electrical currents between the power source and a shunt device,the shunt device comprising an electrically resistive load.
 2. Themethod of claim 1, further comprising matching, with one or morecapacitors coupled in parallel with the one or more of the plurality ofcoils, a frequency of the magnetic field generated by the at least onerecharging coil with a resonant frequency of a tank circuit formed bythe one or more capacitors coupled in parallel with the one or more ofthe plurality of coils.
 3. The method of claim 1, further comprisingpreventing, with one or more diodes coupled to the one or more of theplurality of coils, the one or more electrical currents induced in theone or more plurality of coils from being backward driven into anotherof the plurality of coils.
 4. The method of claim 1, further comprisingsensing, with sensing circuitry, each of the one or more electricalcurrents induced in the one or more plurality of coils.
 5. The method ofclaim 1, wherein each of the first coil, the second coil, and the thirdcoil encircle a portion of a ferrite core, and wherein the third coilencircles at least a portion of the first coil and the second coil, andwherein the second coil encircles at least a portion of the first coil.6. The method of claim 1, further comprising: determining that thesummed one or more electrical currents induced into the plurality ofcoils is not to be applied to the power source; and responsive todetermining the summed one or more electrical currents is not to beapplied to the power source, shunting, with the shunt device coupled inparallel with the power source, the summed one or more electricalcurrents.
 7. The method of claim 1, wherein the medical device isimplanted within the patient.
 8. The method of claim 1, wherein thefirst axis, the second axis, and the third axis are orthogonal.
 9. Amedical device configured to be within a patient, the medical devicecomprising: a rechargeable power source configured to provide electricalpower to the medical device; a multi-axis antenna comprising a pluralityof coils encircling a ferrite core, the multi-axis antenna configured togenerate a recharging current from one or more electrical currentsinduced into one or more of the plurality of coils when an externallygenerated magnetic field having a magnetic field direction is imposedonto the multi-axis antenna, wherein the plurality of coils comprises afirst coil having a first coil axis of orientation and formed from firstelectrically conductive winding, a second coil having a second coil axisof orientation and formed from a second electrically conductive winding,and a third coil having a third coil axis of orientation and formed froma third electrically conductive winding; one or more diodes coupled toone or more of the plurality of coils and configured to prevent the oneor more electrical currents induced into the one or more of theplurality of coils from being backward driven into another of the one ormore of the plurality of coils; recharging circuitry coupled to themulti-axis antenna and to the rechargeable power source, the rechargingcircuitry configured to direct a sum of the one or more electricalcurrents induced in one or more of the plurality of coils into therechargeable power source; and a switching device, coupled to therecharging circuitry and the multi-axis antenna, the switching deviceconfigured to switch the sum of the one or more electrical currentsbetween the rechargeable power source and a shunt device, the shuntdevice comprising an electrically resistive load.
 10. The medical deviceof claim 9, further comprising one or more capacitors coupled inparallel with the one or more of the plurality of coils to match afrequency of the magnetic field generated externally with a resonantfrequency of a tank circuit formed by the one or more capacitors coupledin parallel with the one or more of the plurality of coils.
 11. Themedical device of claim 9, wherein the one or more diodes are configuredto rectify the one or more electrical currents induced in the one ormore plurality of coils.
 12. The medical device of claim 9, furthercomprising sensing circuitry coupled to the recharging circuitry and themulti-axis antenna that senses the one or more electrical currentsinduced in the one or more plurality of coils.
 13. The medical device ofclaim 9, wherein each of the first coil, the second coil, and the thirdcoil encircle a portion of the ferrite core, and wherein the third coilencircles at least a portion of the first coil and the second coil, andwherein the second coil encircles at least a portion of the first coil.14. The medical device of claim 9, wherein the first axis, the secondaxis, and the third axis are orthogonal.
 15. A recharging system forrecharging a rechargeable power source located in a medical deviceinternal to a patient, the recharging system comprising: an electricalpower source; at least one recharging coil coupled to the electricalpower source and configured to generate a magnetic field having amagnetic field direction and frequency when electrically energized bythe electrical power source; a multi-axis antenna located in the medicaldevice, the multi-axis antenna comprising a plurality of coilsconfigured to generate a recharging current when the magnetic fieldgenerated by the at least one recharging coil is imposed onto themulti-axis antenna, wherein the plurality of coils comprises a firstcoil having a first coil axis of orientation, a second coil having asecond coil axis of orientation, and a third coil having a third coilaxis of orientation; one or more capacitors coupled in parallel with oneor more of the plurality of coils, where the one or more capacitors areconfigured to have a resonant frequency that matches the magnetic fieldfrequency applied by the at least one recharging coil; a common node tothe plurality of coils, the common node configured to sum one or morecurrents induced into one or more of the first coil, the second coil,and the third coil to generate the recharging current; and a switchingdevice coupled to the multi-axis antenna, the rechargeable power sourceof the medical device, and a shunt device, the switching deviceconfigured to be controlled by recharging circuitry to couple therecharging current to the rechargeable power source to recharge theelectrical energy stored in the rechargeable power source, or to couplethe recharging current to the shunt device, and the shunt devicecomprising an electrically resistive load.
 16. The system of claim 15,further comprising one or more diodes coupled to one or more of theplurality of coils, the one or more diodes configured to rectify the oneor more currents induced in the one or more plurality of coils.
 17. Thesystem of claim 15, further comprising sensing circuitry coupled to therecharging circuitry and the multi-axis antenna that senses the one ormore currents induced in the one or more plurality of coils.